Refactor Platforms/WASI/__main__.py for lazy importing and future new subcommands

[brettcannon]

Everything related to the build subcommand & friends has been moved into a _build module which is now lazily imported in __main__ which now only handles argparse. This did require tweaking what the defaults are in the argument parser so that it didn't trigger needing to import _build. It also required changing dispatching to subcommands from a dict to a match statement to also avoid triggering the import of _build. As well, all imports in _build that are not needed for every subcommand has also been made lazy. Since neither PEP 8 or Ruff/Black have decided how to sort lazy imports, they are interleaved and imports are sorted by name as if the lazy aspect of the statement wasn't there.

This work also sets things up so that any future subcommands can go into their own module and also be lazily imported into __main__.

[hugovk]

Since neither PEP 8 or Ruff/Black have decided how to sort lazy imports,

Ruff and isort issues:

• Support and lints for lazy imports in Python 3.15+ astral-sh/ruff#21305
• Support explicit lazy imports in Python 3.15 (PEP 810) PyCQA/isort#2462

they are interleaved and imports are sorted by name as if the lazy aspect of the statement wasn't there.

Although this PR is using __lazy_modules__ and not the lazy keyword.

[hugovk]

Now we have this duplicate:

      - id: ruff-check
        name: Run Ruff (lint) on Tools/build/
        args: [--exit-non-zero-on-fix, --config=Tools/build/.ruff.toml]
        files: ^Tools/build/
      - id: ruff-check
        name: Run Ruff (lint) on Tools/build/
        args: [--exit-non-zero-on-fix, --config=Tools/build/.ruff.toml]
        files: ^Tools/build/

[brettcannon]

they are interleaved and imports are sorted by name as if the lazy aspect of the statement wasn't there.

Although this PR is using __lazy_modules__ and not the lazy keyword.

Correct! (The initial version did, but I realized backporting would not be fun with lazy, so I went with __lazy_modules__.)

Maybe that will help define what to do with lazy as sorting differently based on whether __lazy_modules__ or lazy is used might be a little too weird.