WASM build

[eitsupi]

Unlike extendr, savvy can be built for webR, so the next branch should be able to do the same thing as pola-rs/polars#20383.
In fact, R-universe CI successfully building for webR until I incorporated the parquet feature of polars (although it didn't seem to work due to what appeared to be threading issues).
It seems that savvy does not require the new LLVM, unlike pyo3.

cc @georgestagg

[georgestagg]

Note that in pola-rs/polars#20383 we also disable the parquet feature for the Pyodide build, along with some other Rust features that cause issues right now. I expect this can be improved in time except for the cloud related features, which might be difficult to get working in the Wasm sandbox.

Re: threading, the thread pool should be limited to a single thread when running under Emscripten now (set here), but there may still be some configuration tweaks along these lines required to compile for webR. It is important in webR not to compile/link with -pthreads at all.

[eitsupi]

Thanks George, the test build on R-universe (from eitsupi/neo-r-polars#50) seems working.

> install.packages("rlang")
Downloading webR package: rlang
> install.packages("neopolars", repos = "https://eitsupi.r-universe.dev")
Downloading webR package: neopolars
> library(neopolars)
> as_polars_df(mtcars)$select("cyl", "am")
shape: (32, 2)
┌─────┬─────┐
│ cyl ┆ am  │
│ --- ┆ --- │
│ f64 ┆ f64 │
╞═════╪═════╡
│ 6.0 ┆ 1.0 │
│ 6.0 ┆ 1.0 │
│ 4.0 ┆ 1.0 │
│ 6.0 ┆ 0.0 │
│ 8.0 ┆ 0.0 │
│ …   ┆ …   │
│ 4.0 ┆ 1.0 │
│ 8.0 ┆ 1.0 │
│ 6.0 ┆ 1.0 │
│ 8.0 ┆ 1.0 │
│ 4.0 ┆ 1.0 │
└─────┴─────┘

[eitsupi]

Done by b900d63