Bump spec engine target seam

[MaxGhenis]

Summary

• bump the packaged US spec dependency on microplex from 90f21d2 to 2e56012
• keep uv.lock in sync so the spec pack resolves to the engine with run_spec TargetProvider support

Checks

• env -u UV_FROZEN uv lock
• env -u UV_FROZEN uv run --extra dev python -m pytest tests/specs/test_us_2024_spec.py tests/test_project_metadata.py -q
• env -u UV_FROZEN uv run --extra dev ruff check tests/specs/test_us_2024_spec.py src/microplex_us/specs/init.py
• env -u UV_FROZEN uv build --wheel --out-dir /tmp/microplex_us_spec_target_seam_wheel_check
• unzip -l /tmp/microplex_us_spec_target_seam_wheel_check/microplex_us-0.2.0-py3-none-any.whl | rg 'microplex_us/specs/us-2024.yaml'