Pre-release 0.2.11b1: decouple extension metadata from wheel==0.30.0

[aryasadeghi1]

Summary

Replaces the legacy wheel==0.30.0 metadata.json read path with pkginfo-based METADATA parsing, so the Azure CLI ecosystem can move off the wheel==0.30.0 and setuptools==70.0.0 pins.

Impacts

• Unblocks upgrading setuptools past the ==70.0.0 pin, which is required to pick up the fix for CVE-2025-47273 (path traversal, fixed in setuptools 78.1.1). Context: {Package} Upgrade setuptools and wheel to the latest version. azure-cli-extensions#7740.
• Removes a transitive dep on a 7-year-old wheel release.

Approach

Picks up from #521 (thanks @wangzelin007), but per @jiasli's review comment the implementation now uses pkginfo.Wheel instead of vendoring wheel 0.30.0 internals.

• New module azdev/operations/extensions/metadata.py with pkginfo_to_dict and merge_to_index_metadata.
• get_ext_metadata in util.py now reads METADATA via pkginfo and merges azext-only keys on top, eliminating the dependency on the legacy metadata.json artifact (no longer emitted by modern wheel).
• setup.py: drops wheel==0.30.0 and setuptools==70.0.0; adds pkginfo and setuptools>=78.1.1,<80 (upper bound preserves setup.py develop for unmigrated extensions).
• Bumps version to 0.2.11b1 (pre-release) so we can validate before promoting to 0.2.11 (release).

Tests

azdev/operations/tests/test_metadata.py:

• Unit tests for pkginfo_to_dict, merge_to_index_metadata, _coerce_run_requires (handling metadata duplication), and the azext-override precedence.
• Golden-comparison test (ported from Pre-release: extract metadata generation logic and decouple from wheel 0.30.0 #521): downloads the real azure_cli_ml-1.41.0 wheel and DeepDiffs the generated metadata against the historical index.json block. Fields that wheel 0.30.0 only ever emitted via its side-channel metadata.json. Test skips on network failure.

Supersedes #521.
Closes #521.