Allow lists in `pyodide config`

[agriyakhetarpal]

It would be great if we could support List types in pyodide_build.config.DEFAULT_CONFIG. The question is how to support the list type in an env variable.

Originally posted by @ryanking13 in #187 (comment)

[agriyakhetarpal]

So, if we do this, it would allow us to use something like:

[tool.pyodide.build]
ignored_build_requirements = ["patchelf", "oldest-supported-numpy", "cmake", "my-ignored-package"]

instead of the current representation where we need to use a single concatenated string.

One thing we could do is to allow lists for configuration variables listed in pyproject.toml only, and keep using strings for configuration variables supplied as environment variables, but that introduces a bit of complexity – and I'm sure there are never going to be a lot of cases where a configuration option needs to have multiple values in a list.

N.B. cibuildwheel also suffers from the same limitation.

[ryanking13]

Yeah, I think we can revisit this when we have more configurations with similar requirements. For now using concatenated string seems okay to me.