Handle dictionary keys that cannot be sorted in has_entries

[ryanduguid]

Summary

Allow has_entries to match dictionaries with mixed or unordered keys, including frozen dataclass instances. Preserve sorted descriptions and matcher evaluation order when sorting succeeds; use the original item order when comparisons raise TypeError.

items = list(value_matchers.items())
try:
    ordered_items = sorted(items)
except TypeError:
    ordered_items = items

Fixes #271. Add ten regression tests and a changelog fragment.

Evidence

• Before: The initial regression run against the original runtime produces seven failing outcomes and 22 passes, including subtests. Mixed and frozen dataclass keys raise TypeError during construction.
  After: The focused suite passes all 27 tests. Coverage includes descriptions, first mismatch, evaluation order, input preservation, one-shot item iteration and exception boundaries.
• Linux uv tool run tox -s: all 20 configured environments pass, including typing, lint, documentation, package description, changelog and coverage. CPython 3.10 through 3.14 each passes 456 tests with 14 NumPy skips, or 470 with NumPy. The four PyPy aliases each pass 448 tests with 15 skips and all resolve to PyPy 3.10.16.
• Windows Python 3.14: 456 tests pass with 14 skips and two warnings; the configured lint target passes. Deliberate mutations that retry item acquisition, evaluate a second value after the first failure, or sort the fallback list in place fail the corresponding regression assertions.
• Documentation builds successfully with 274 warnings. Coverage reports 98% for the changed runtime file and no partial branches.

Risk

The fallback also absorbs TypeError raised by a custom comparison method. Errors from obtaining or materialising items, other comparison exceptions and value matcher exceptions still propagate. Fallback descriptions and the first mismatch follow the supplied item order.

Unverified

PyPy, macOS and other Windows Python versions were not run. Documentation warnings were not compared with master. Hosted CI has not run.

[offbyone]

Barring a few very specific examples, the tests in this repo go through the factory functions (has_entries) without directly instantiating the matcher object. I would prefer to keep that pattern unless there's a compelling reason not to, and I don't see one here.

[ryanduguid]

Moved the coverage to has_entries and dropped the three tests that built IsDictContainingEntries directly (e748f27).

[ryanduguid]

@offbyone the tests now go through has_entries only (e748f27), as you asked. I have also reverted two unrelated workflow commits that had been added to this branch (d95eaa2), so the diff is back to the fix, its tests and the changelog fragment. Could you take another look when you have time?