refactor: reuse shared grid layers in Q7 parser

[tubededentifrice]

Summary

Keeps the Q7 shared-grid reuse from #848 as a small parser-internal refactor. The draft no longer expands the Q7 trait API and remains independent of the Q10 map stack.

Changes

• Classify Q7 SCMap cells into the shared background, wall, and floor classes.
• Build GridLayers once inside B01MapParser.parse from the already-parsed protobuf payload.
• Render the existing composed Q7 image from those internal canonical layers.
• Keep MapContentTrait unchanged: callers continue to receive only image_content, map_data, and raw_api_response.
• Remove speculative Q7 calibration; no current Q7 renderer or caller consumes it.

Review feedback addressed

• Layers and calibration are no longer exposed as public trait fields.
• The trait no longer reparses the raw map payload.
• Shared decomposition stays behind the existing parser interface and is used directly by rendering.

Validation

• focused Q7 parser and trait suite — 39 passed
• pytest -q — 792 passed, 86 snapshots passed
• pre-commit run --show-diff-on-failure --color=always --all-files — all hooks passed, including Ruff and mypy

[allenporter]

I know this is draft still and not ready but giving early feedback in the name of quick iteration

[allenporter]

These don't seem like data points we want or need to expose to callers, and are more like internal map rendering details.

[allenporter]

Once parsed, these don't appear to be used by anything.

is there a specifc reason we're parsing the raw payload again? I would expect this to all be behind the existing self._map_parser.parse call above where the map parser parses the raw content and pulls out useful data points.

Is it because in q10 these come as a separate channel, therefore we need to change the map interface from working in raw payload to be raw payload + layers + calibration data?