fix(model-bridge): restore native state dict round trips

[mikemikimike]

Summary

• Restore TransformerBridge.state_dict() round trips through the native/raw model.
• Map each TransformerLens key back to all underlying aliased raw keys before loading.
• Preserve direct clean/native key loading for Tracr-style state dicts.
• Respect strict=True instead of silently downgrading strict loads.
• Add regression coverage for round trips, strict missing-key failures, and raw native keys.

Fixes #1587

Validation

• PYTHONUTF8=1 uv run pytest tests/unit -m "not slow" -n 4 -q — 5,165 passed, 57 skipped, 10 xfailed
• PYTHONUTF8=1 uv run pytest tests/unit/model_bridge/test_boot_native.py -q — 28 passed
• uv run mypy . — passed, 421 source files
• uv run pycln --check ... — passed
• uv run isort --check-only ... — passed
• uv run black --check ... — passed
• git diff --check — passed

The focused tests/integration/model_bridge run was attempted locally but exceeded the 15-minute execution limit without producing a test assertion failure; the unit suite and targeted regression suite completed successfully.