Updates stitcher to trim all edges evenly rather than right/bottom only.

[palmhjell]

The stitcher currently trims each tile by adjusting the size of the image (e.g., tile.shape[-1] - overlap) which only cuts off one side of each tile rather than trimming it symmetrically. When the image has some vignetting or other artifacts on the edges, these would get carried over to each tile rather than being trimmed evenly and interfere with the chamber images.

For example, residual darkness from the neutral density filter on Setup 7 (which annoyingly remains even when the filter is fully open) is retained at the top of each chamber here and effectively cuts many chambers in half across full rows:

Adjusting the trimming operation to trim each edge of the image symmetrically gives much better images:

This PR implements this fix and handles overlap values that are 0 or odd.

[k-rl]

Looks good just one small comment + fixing the ruff issues and we're good to merge :)

[k-rl]

Rather than checking for this condition could you do the same thing I did in the previous version of the code which is to just have:

tiles = assay.tile[
    ...,
    clip : assay.tile.shape[-2] - clip + remainder,
    clip : assay.tile.shape[-1] - clip + remainder,
]

That way you're minimizing how much branching happens in the code which makes it easier to reason about. If you're concerned about a bug being introduced later on when the code gets changed because of the tricky indexing you can leave a comment explaining that we're intentionally not using the negative endpoint indexing here because of when self. overlap is 0.