fix: correctly handle absolute URLs in parse_simpleapi_html.bzl

[WSUFan]

This PR addresses a typo and improves the handling of absolute URLs in the
parse_simpleapi_html.bzl file and corrects a minor issue in the
simpleapi_download.bzl file.

Summary:

1. parse_simpleapi_html.bzl:

   • Introduced a new private function _get_root_directory(url) to extract
     the root directory from a given URL.
   • Enhanced _absolute_url function to correctly handle absolute URLs by
     utilizing the _get_root_directory function. This ensures that URLs
     starting with a "/" are correctly resolved to their full path, avoiding
     potential incorrect concatenation.

2. simpleapi_download.bzl: Corrected the handling of the real_url variable in
   the _read_simpleapi function, ensuring that the correct URL is passed to
   _read_index_result when using non-blocking downloads.

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[aignas]

Could you please add a test in https://github.com/bazelbuild/rules_python/blob/3b183bfedd3dd6a5bb42c77531079e347165441d/tests/pypi/parse_simpleapi_html/parse_simpleapi_html_tests.bzl so that this does not regress?

And please add a note in the Changelog.md file.

[WSUFan]

Could you please add a test in https://github.com/bazelbuild/rules_python/blob/3b183bfedd3dd6a5bb42c77531079e347165441d/tests/pypi/parse_simpleapi_html/parse_simpleapi_html_tests.bzl so that this does not regress?

And please add a note in the Changelog.md file.

Yeah. Sure. I will do it. Thanks!

[WSUFan]

Could you please add a test in https://github.com/bazelbuild/rules_python/blob/3b183bfedd3dd6a5bb42c77531079e347165441d/tests/pypi/parse_simpleapi_html/parse_simpleapi_html_tests.bzl so that this does not regress?

And please add a note in the Changelog.md file.

Hi @aignas, I have added tests and changed the Changelog.md. Please take a look when you get a chance. Let me know if you have other concerns. Thanks!

[aignas]

LGTM, thank you.

The current structure is alright, we can optimize the code if we see any problems later. At the end of the day, when using the MODULE.bazel.lock file, this code will be executed only when the PyPI dependencies change and the time spent querying the PyPI server itself is greater than the time spent parsing it.

Thank you very much for the contribution!