Post-join panic on select after joining on keys with different names with "coalesce=False"

[alexander-beedie]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

Python:

(DataFrame API)

import polars as pl

lf1 = pl.LazyFrame({"x": [-1, 0, 1, 2, 3, 4]})
lf2 = pl.LazyFrame({"y": [0, 1, -2, 3, 5, 6]})
lf3 = lf1.join(lf2, how="inner", left_on="x", right_on="y", coalesce=False)

lf3.collect()
# shape: (3, 2)
# ┌─────┬─────┐
# │ x   ┆ y   │  << definitely have column "y"
# │ --- ┆ --- │
# │ i64 ┆ i64 │
# ╞═════╪═════╡
# │ 0   ┆ 0   │
# │ 1   ┆ 1   │
# │ 3   ┆ 3   │
# └─────┴─────┘

lf3.select("y").collect()
# pyo3_runtime.PanicException: called `Result::unwrap()` 
#  on an `Err` value: ColumnNotFound(ErrString("y"))

Rust:

(SQL context, if on this PR's branch #16507; also happens with regular API)

let df1 = df! {"x" => [-1, 0, 1, 2, 3, 4]}.unwrap();
let df2 = df! {"y" => [0, 1, -2, 3, 5, 6]}.unwrap();

let mut ctx = SQLContext::new();
ctx.register("df1", df1.lazy());
ctx.register("df2", df2.lazy());

// join on x = y
let sql = r#"
    SELECT df2.*
    FROM df1
    INNER JOIN df2 ON df1.x = df2.y
    ORDER BY y
"#;
let df3 = ctx.execute(sql).unwrap().collect().unwrap();

Log output

thread '...' panicked at crates/polars-plan/src/utils.rs:371:79:
called `Result::unwrap()` on an `Err` value: ColumnNotFound(ErrString("y"))
stack backtrace:
   0: rust_begin_unwind
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_fmt
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/panicking.rs:72:14
   2: core::result::unwrap_failed
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/result.rs:1654:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/result.rs:1077:23
   4: polars_plan::utils::expr_irs_to_schema::{{closure}}
             at /Users/.../polars/crates/polars-plan/src/utils.rs:371:29
   5: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/ops/function.rs:305:13
   6: core::option::Option<T>::map
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/option.rs:1072:29
   7: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/iter/adapters/map.rs:108:26
   8: <polars_core::schema::Schema as core::iter::traits::collect::FromIterator<F>>::from_iter
             at /Users/.../polars/crates/polars-core/src/schema.rs:59:20
   9: core::iter::traits::iterator::Iterator::collect
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/iter/traits/iterator.rs:2005:9
  10: polars_plan::utils::expr_irs_to_schema
             at /Users/.../polars/crates/polars-plan/src/utils.rs:368:5
  11: polars_plan::logical_plan::builder_ir::IRBuilder::project
             at /Users/.../polars/crates/polars-plan/src/logical_plan/builder_ir.rs:50:17
  12: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::finish_node
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/mod.rs:206:13
  13: polars_plan::logical_plan::optimizer::projection_pushdown::projection::process_projection
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/projection.rs:125:14
  14: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down::{{closure}}
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/mod.rs:330:43
  15: stacker::maybe_grow
             at /Users/a13107q/.cargo/registry/src/index.crates.io-6f17d22bba15001f/stacker-0.1.15/src/lib.rs:55:9
  16: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/mod.rs:315:5
  17: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::optimize
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/mod.rs:723:9
  18: polars_plan::logical_plan::optimizer::optimize
             at /Users/.../polars/crates/polars-plan/src/logical_plan/optimizer/mod.rs:144:19
  19: polars_lazy::frame::LazyFrame::optimize_with_scratch
             at /Users/.../polars/crates/polars-lazy/src/frame/mod.rs:549:22
  20: polars_lazy::frame::LazyFrame::prepare_collect_post_opt
             at /Users/.../polars/crates/polars-lazy/src/frame/mod.rs:602:13
  21: polars_lazy::frame::LazyFrame::_collect_post_opt
             at /Users/.../polars/crates/polars-lazy/src/frame/mod.rs:623:49
  22: polars_lazy::frame::LazyFrame::collect
             at /Users/.../polars/crates/polars-lazy/src/frame/mod.rs:653:9
  23: polars_sql::context::SQLContext::execute_select
             at ./src/context.rs:455:14
  24: polars_sql::context::SQLContext::process_set_expr
             at ./src/context.rs:205:45
  25: polars_sql::context::SQLContext::execute_query_no_ctes
             at ./src/context.rs:173:18
  26: polars_sql::context::SQLContext::execute_query
             at ./src/context.rs:169:9
  27: polars_sql::context::SQLContext::execute_statement
             at ./src/context.rs:151:40
  28: polars_sql::context::SQLContext::execute
             at ./src/context.rs:119:19
  29: statements::test_join_on_different_keys
             at ./tests/statements.rs:512:18
  30: statements::test_join_on_different_keys::{{closure}}
             at ./tests/statements.rs:497:33
  31: core::ops::function::FnOnce::call_once
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/ops/function.rs:250:5
  32: core::ops::function::FnOnce::call_once
             at /rustc/ab14f944afe4234db378ced3801e637eae6c0f30/library/core/src/ops/function.rs:250:5

Issue description

Selecting a valid column after a join where "coalesce=False" can result in a panic.

Expected behavior

Return the following frame:

# shape: (3, 1)
# ┌─────┐
# │ y   │
# │ --- │
# │ i64 │
# ╞═════╡
# │ 0   │
# │ 1   │
# │ 3   │
# └─────┘

Installed versions

Compiled from latest main with all standard features.
Also confirmed on latest 0.20.30 release build.