Fix modal feed recovery for resume-at-line

[righteousgambit]

Closes #669

Summary

Recover modal feed words independently of motion-command formatting so resume-at-line can restore standalone and tightly packed F values before recovery movement.

Changes

• Scan prior lines with the controller's existing G-code tokenizer instead of requiring a recognized G1/G2/G3 prefix.
• Select the most recent valid F token while continuing to ignore comments.
• Add unit coverage for standalone F, tightly packed G-code, comments, and recovery-command ordering.
• Add an unreleased changelog entry.

Why

Feed is modal independently of a motion word. The previous parser could skip a valid F275 line or a packed X10Y10G1F425 line, then restore an older feed before the resume recovery Z move.

The motion risk is conditional on retained controller state; the fix makes the recovery value explicit and deterministic.

Validation

• Regression against the pinned develop implementation: 3 failed, 2 passed; standalone and packed feed values incorrectly resolved to the older 100, and the preview omitted buffer G1 F275.
• With this change, using the same exact-ref sparse harness: PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=/tmp/carvera-test-stubs:. pytest -q tests/unit/test_resume_feed_rate.py -> 5 passed.
• ruff check carveracontroller/Controller.py tests/unit -> passed.
• git diff --check develop...HEAD -> passed.

Real branch verification

The repository's locked Poetry environment was installed from poetry.lock. The targeted suite passed on real fork commit 7df0e9867548, whose sole parent is pinned upstream develop@2ea66c10e96d88013a04441134d3d4f8e8c88510.

poetry run pytest -q tests/unit/test_resume_feed_rate.py

Result: 5 passed.

Quality gates on the real branch:

• Ruff check: passed
• Ruff format --check: passed
• git diff --check 2ea66c10e96d88013a04441134d3d4f8e8c88510..7df0e9867548884728170818e3ee34d873eaecae: passed