Fix descending uniform-coordinate binned selection in ImageTool

[kmnhan]

Summary

• Clamp ImageTool bin slices at array boundaries so edge cursors no longer produce empty selections.
• Make qsel_args_from_indexers safe for descending uniform coordinates by rejecting empty bins early, emitting non-negative widths, and validating against reversed slice bounds when needed.
• Reuse the boundary-safe slice logic in both hidden-axis binning paths so xslice and averaged selection stay consistent.
• Add regressions for descending-coordinate binning, qsel reconstruction, and xslice near a boundary.

Testing

• Not run (not requested)
• Added unit regressions covering _bin_slice, qsel_args_from_indexers, and xslice on descending uniform coordinates.

[Copilot]

Pull request overview

Fixes an ImageTool bug where binning at the boundary of a descending uniform coordinate produced empty selections, and makes qsel_args_from_indexers correctly handle descending coordinates by always emitting non-negative bin widths and validating against a reversed slice.

Changes:

• Clamp/redistribute _bin_slice bounds at array boundaries so edge cursors don't yield empty windows.
• Make qsel_args_from_indexers produce non-negative widths and validate using a reversed slice for descending coords.
• Reuse _bin_slice in both hidden-axis binning paths (_bin_along_axis / _bin_along_multiaxis) to keep slicing consistent.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/erlab/interactive/imagetool/slicer.py	Boundary clamping in _bin_slice, descending-coord safety in qsel_args_from_indexers, and reuse of _bin_slice in binning helpers.
tests/interactive/imagetool/test_slicer.py	Adds regressions for boundary _bin_slice, descending-coord qsel_args_from_indexers, and xslice with descending hidden axis.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.89%. Comparing base (f966c25) to head (d3a6910).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/erlab/interactive/imagetool/slicer.py	94.73%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #376   +/-   ##
=======================================
  Coverage   88.89%   88.89%           
=======================================
  Files         139      139           
  Lines       47155    47165   +10     
  Branches     7588     7592    +4     
=======================================
+ Hits        41918    41927    +9     
  Misses       3271     3271           
- Partials     1966     1967    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.