[TomCC7]

Add plain generated OccupancyGrid helpers for array/file input, read-only row-major views, rotated map coordinates and explicit Header timestamps. This prepares the mapping/navigation cutover without replacing the existing grid class or changing existing consumers yet.

Parent: #4668. Part of the message encoding refactor.

Area	Change
Generated occupancy helper	Validated ROS cells/resolution, safe NumPy loading, PNG unknown-cell mapping, independent input copies, rotated coordinate conversion
Legacy grid module	Move the existing CostValues and identical block_max_reduce implementation into the shared helper; retain their old import names and the legacy grid class
Tests/workflow	Actual CDR/MCAP round trips, complete embedded schema closure, zero/negative/epoch timestamps, input ownership and current legacy regression coverage
Navigation doc link	Disambiguate an existing filename label after adding the new occupancy helper

From an installed main-package wheel for this proposal, the generated value workflow is:

import numpy as np
from dimos_cdrgen.registry import decode, encode
from dimos.messages.builtin_interfaces.msg import Time
from dimos.messages.nav_msgs.msg import OccupancyGrid
from dimos.messages.std_msgs.msg import Header
from dimos.msgs.occupancy import occupancy_from_array, occupancy_view

grid = occupancy_from_array(
    np.array([[-1, 0, 100]], dtype=np.int8), resolution=0.25,
    header=Header(frame_id="map", stamp=Time(sec=0, nanosec=1)),
)
received = decode(encode(grid), OccupancyGrid)
assert occupancy_view(received).tolist() == [[-1, 0, 100]]
assert received.header.stamp.nanosec == 1

For a prepared checkout, run the focused checks with python -m pytest --noconftest -o addopts='' -q dimos/msgs/test_occupancy.py dimos/msgs/nav_msgs/test_OccupancyGrid.py.

Validation: 41 source cases pass, including the retained historical pointcloud fixture case. That project LFS archive was fetched once, SHA256 verified against its pointer (245395d0c3e200fcfcea8de5de217f645362b145b200c81abc3862e0afc1aa7e,327201 bytes), and safely extracted (898117 bytes). Installed-main-wheel checks pass 40 cases with the generated production helper asserted to come from site-packages; the source-only fixture lookup case is deselected in that installed run. One production helper passes strict typing, applicable hooks pass, normal main wheel builds and the default 198-package environment passes pip check. Wheel SHA256 ea88584c175a0fcb4735ba1133b7ae58abb9683491cdc86f788e933943d756bd.

This layer does not switch mapping/navigation producers, default encoding or remove legacy recording/classes. No hardware, benchmark investigation or CI polling performed.