This just cleans up the code and moves more logic from the
repository_rule
(i.e. generation of `BUILD.bazel` files) to loading time (macro
evaluation).
This makes the unit testing easier and I plan to also move the code that
is
generating config setting names from filenames to this new macro, but
wanted to
submit this PR to reduce the review chunks.

Summary:
- Add a new `pkg_aliases` macro.
- Move logic and tests for creating WORKSPACE aliases.
- Move logic and tests bzlmod aliases.
- Move logic and tests bzlmod aliases with groups.
- Add a test for extra alias creation.
- Use `whl_alias` in `pypi` extension integration tests.
- Improve the serialization of `whl_alias` for passing to the pypi hub
repo.

Related to #260, #2386, #2337, #2319 - hopefully cleaning the code up
will make
it easier to address those feature requests later.

---------

Co-authored-by: Richard Levasseur <richardlev@gmail.com>

Before hand we would pass around `whl_alias` struct instances and it
would go through rounds of starlark functions which would end up
rendered as BUILD.bazel files in the hub repository. This means that
every time the output of the said functions would change, the
`MODULE.bazel.lock` would also possibly change.

Since we now have much better unit testing framework, we start relying
on these functions being evaluated at loading phase instead of repo rule
phase, which means that we can make the `BUILD.bazel` files not change a
lot when the underlying code changes, this should make the code more
maintainable in the long run and unblocks the code to accept extra
things, like env marker values or similar.

Summary:
- Remove the `repo` field from `whl_alias`.
- Rename `whl_alias` to `whl_config_setting`
- Move the tests around
- Simplify the `pkg_aliases` tests to use `contains` instead of exact
  equality to make things less brittle.
- Simplify the `pkg_aliases` tests to use different mocks to make
  expectations easier to understand.
- Make `whl_config_setting` hashable by using tuples instead of lists.

This is definitely needed for bazelbuild#2319 and bazelbuild#2423.

Before hand we would pass around `whl_alias` struct instances and it
would go through rounds of starlark functions which would end up
rendered as BUILD.bazel files in the hub repository. This means that
every time the output of the said functions would change, the
`MODULE.bazel.lock` would also possibly change.

Since we now have much better unit testing framework, we start relying
on these functions being evaluated at loading phase instead of repo rule
phase, which means that we can make the `BUILD.bazel` files not change a
lot when the underlying code changes, this should make the code more
maintainable in the long run and unblocks the code to accept extra
things, like env marker values or similar.

Summary:
- Remove the `repo` field from `whl_alias`.
- Rename `whl_alias` to `whl_config_setting`
- Move the tests around
- Simplify the `pkg_aliases` tests to use `contains` instead of exact
  equality to make things less brittle.
- Simplify the `pkg_aliases` tests to use different mocks to make
  expectations easier to understand.
- Make `whl_config_setting` hashable by using tuples instead of lists.

This is definitely needed for bazelbuild#2319 and bazelbuild#2423.