test: cover deprecated Hooked model loaders

[tomatotomata]

What changed

Added one regression test for each deprecated Hooked*.from_pretrained path on dev-4.x, asserting the warning names the legacy class and points to TransformerBridge.boot_transformers(...).

Added a narrowly scoped pytest warning filter for those known internal compatibility warnings. The tests use pytest.warns, so they continue to observe the warning instead of hiding regressions.

Validation

• pytest tests/unit/test_deprecation_warnings.py -q: 3 passed.
• black --check tests/unit/test_deprecation_warnings.py: passed.
• mypy . --no-incremental: passed with no issues in 417 source files.
• Unit-test collection succeeds with 5,205 tests after the sparse checkout was completed.
• The full tests/unit -m "not slow" run exceeded four minutes locally, so the repository CI matrix should provide the full-suite result.

Closes #1564

[jlarson4]

@tomatotomata Is this ready for review?

[jlarson4]

Closing, as we have another PR that is covering this issue. Thanks for working on this @tomatotomata!