Add tests for package_search (#2092)

[ahlbertng]

Description

This PR adds unit tests for src/rez/package_search.py, which currently has no test coverage (as noted in #2092).

Addresses part of #2092.

What's tested

get_reverse_dependency_tree()
Correctly builds a reverse dependency tree for a package with known direct dependents
Respects the depth argument (e.g. depth=0 returns only the root package)
ResourceSearcher.search()
Finds all versions of a package family
Returns only the latest version when latest=True
ResourceSearchResultFormatter
Default (no output_format) output correctly shows a package's qualified name
ResourceSearchResult
Correctly stores resource, resource_type, and validation_error (including default None)

Notes

Tests reuse the existing solver/packages test data already used by test_packages.py, so no new test fixtures were added.
get_plugins() is not yet covered, no existing test data currently includes packages with plugin_for set. Open to guidance on whether to add new fixture packages for this, or if there's a preferred approach.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: ahlbertng / name: Ahlbertng (c11bd7b, fba12f5)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.72%. Comparing base (1a83acf) to head (65d0f8d).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2149      +/-   ##
==========================================
+ Coverage   61.31%   61.72%   +0.41%     
==========================================
  Files         164      164              
  Lines       20568    20568              
  Branches     3575     3575              
==========================================
+ Hits        12611    12696      +85     
+ Misses       7085     6983     -102     
- Partials      872      889      +17     

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[maxnbk]

Thank you for the submission of this new set of tests. We really appreciate any added coverage we can squeeze into the repo at this point, especially for such un-tested areas.

I've issued some specific comments attached to areas near the code that they pertain to. These are the main comments I'm making that would flip my recommendation from "don't merge" to "do merge". I made some specific line comments, but the real issue is that the current flake8 linter job fails, so just address those items.

I would express that the largest useful gaps to continue covering, whether they are a part of this PR, or you or anyone else tackles with additional work, would be these:

(Please comment, if you intend to go further with the coverage and aim to address these as well, or if you want to keep this PR self-contained just to the current change-set)

---

test the validate=True path. The ResourceSearcher.search() method has a substantial validate code path with error handling for ResourceContentError. No tests exercise this yet, and is arguably the most complex portion of the module.

test for glob patterns. ResourceSearcher.search() uses fnmatch.fnmatch on the name pattern. A test like searcher.search("py*") would verify the glob codepaths, which is a core feature of the searcher.

test for family resource type. When no version range is specified and multiple families match, the searcher returns resource_type="family". The current tests only exercise the package resource type.