Fix find_bad_channels_maxwell and maxwell_filter cHPI indexing

[christianbrodbeck]

What does this implement/fix?

In find_bad_channels_maxwell, _run_maxwell_filter is called for successive data chunks, but always with the same _MoveComp instance (mc). Inside _run_maxwell_filter , mc.initialize(...) sets up movement compensation starting at the beginning of the whole recording, rather than starting at the beginning of the relevant data chunk. This PR adds an argument to _run_maxwell_filter to use the appropriate data chunk index in the head movement recording.

Similarly, in maxwell_filter, _run_maxwell_filter processes successive data segments separated by annotations, but movement compensation previously advanced only across the processed samples. After a skipped segment, _MoveComp therefore resumed using head positions from before the skip rather than those corresponding to the next data segment. This PR resets movement compensation for each segment using its index in the full recording.

Additional information

Claude Opus 5 identified the issue and assisted in implementing a fix and test. Codex 5.6 Sol reviewed changes.

[larsoner]

Nice! Can I push a commit to add/clean up a bit? Any reason still draft?

[christianbrodbeck]

Now just waiting for CI to pass, feel free to push to clean it up @larsoner

[christianbrodbeck]

Updated the description for the second, related fix