Unify read and scan functions

[stinodego]

read functions should behave exactly like scan functions followed by collect.

There may be some added or removed parameters for functionality that is (not) relevant in eager mode.

We should take a look at our existing scan functions and make sure they conform to these expectations:

• scan_parquet
• Dispatch read_ipc to scan_ipc:
  • This will be a breaking change to storage_options - read_csv and read_ipc do not use native storage_options configuration keys #17815
• Dispatch read_csv to scan_csv:
  • scan_csv currently lacks the following:
    • Support compressed files: #7287
    • scan_csvdoes not support a list of datatypes in schema_overrides #17813
    • Support reading multiple files: #10706
    • Support BytesIO/StringIO: #4950, #12617
      • Can be skipped if it turns out to be too complex
  • This will be a breaking change to storage_options - read_csv and read_ipc do not use native storage_options configuration keys #17815
• scan_ndjson
• scan_delta
• scan_iceberg (has no read equivalent yet)

[Wainberg]

Here are a few open, unaccepted issues that should be addressed during the harmonization of read_csv and scan_csv:

• scan_csv() doesn’t support compressed CSVs, read_csv() does: #7287
• scan_csv() doesn’t support column selection, read_csv() does: #5755
• scan_csv() doesn’t support BytesIO/StringIO, read_csv() does: #4950, #12617
• read_csv() doesn’t support reading multiple files, scan_csv() does: #10706

[mkleinbort-ic]

👍- was about to ask why there is no pl.read_iceberg

On that note - a small documentation recommendation - I think it's time to add sub-headers to the IO functions as grouped by type:

csv: 
- [polars.read_csv](https://docs.pola.rs/py-polars/html/reference/api/polars.read_csv.html)
- [polars.read_csv_batched](https://docs.pola.rs/py-polars/html/reference/api/polars.read_csv_batched.html)
- [polars.scan_csv](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_csv.html)
- [polars.DataFrame.write_csv](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_csv.html)
- [polars.LazyFrame.sink_csv](https://docs.pola.rs/py-polars/html/reference/api/polars.LazyFrame.sink_csv.html)

ipc:
- [polars.read_ipc](https://docs.pola.rs/py-polars/html/reference/api/polars.read_ipc.html)
- [polars.read_ipc_stream](https://docs.pola.rs/py-polars/html/reference/api/polars.read_ipc_stream.html)
- [polars.scan_ipc](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_ipc.html)
- [polars.read_ipc_schema](https://docs.pola.rs/py-polars/html/reference/api/polars.read_ipc_schema.html)
- [polars.DataFrame.write_ipc](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_ipc.html)
- [polars.DataFrame.write_ipc_stream](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_ipc_stream.html)
- [polars.LazyFrame.sink_ipc](https://docs.pola.rs/py-polars/html/reference/api/polars.LazyFrame.sink_ipc.html)

parquet:
- [polars.read_parquet](https://docs.pola.rs/py-polars/html/reference/api/polars.read_parquet.html)
- [polars.scan_parquet](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_parquet.html)
- [polars.read_parquet_schema](https://docs.pola.rs/py-polars/html/reference/api/polars.read_parquet_schema.html)
- [polars.DataFrame.write_parquet](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_parquet.html)
- [polars.LazyFrame.sink_parquet](https://docs.pola.rs/py-polars/html/reference/api/polars.LazyFrame.sink_parquet.html)

database:
- [polars.read_database](https://docs.pola.rs/py-polars/html/reference/api/polars.read_database.html)
- [polars.read_database_uri](https://docs.pola.rs/py-polars/html/reference/api/polars.read_database_uri.html)
- [polars.DataFrame.write_database](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_database.html)

json:
- [polars.read_json](https://docs.pola.rs/py-polars/html/reference/api/polars.read_json.html)
- [polars.read_ndjson](https://docs.pola.rs/py-polars/html/reference/api/polars.read_ndjson.html)
- [polars.scan_ndjson](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_ndjson.html)
- [polars.DataFrame.write_json](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_json.html)
- [polars.DataFrame.write_ndjson](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_ndjson.html)
- [polars.LazyFrame.sink_ndjson](https://docs.pola.rs/py-polars/html/reference/api/polars.LazyFrame.sink_ndjson.html)

avro:
- [polars.read_avro](https://docs.pola.rs/py-polars/html/reference/api/polars.read_avro.html)
- [polars.DataFrame.write_avro](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_avro.html)

excel:
- [polars.read_excel](https://docs.pola.rs/py-polars/html/reference/api/polars.read_excel.html)
- [polars.read_ods](https://docs.pola.rs/py-polars/html/reference/api/polars.read_ods.html)
- [polars.DataFrame.write_excel](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_excel.html#)

iceberg:
- [polars.scan_iceberg](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_iceberg.html)

delta:
- [polars.scan_delta](https://docs.pola.rs/py-polars/html/reference/api/polars.scan_delta.html)
- [polars.read_delta](https://docs.pola.rs/py-polars/html/reference/api/polars.read_delta.html)
- [polars.DataFrame.write_delta](https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_delta.html)

...