Restore signal monitoring in long-running accelerator operations

[mdekstrand]

This updates progress in long-running accelerator operations to also check for Python signals again.

• Add process_iter (and a variant with an explicit counter) to process an iterator in a worker thread, using rayon-cancel to cancel operation.
• Monitor for cancellation signals in main thread, since that is where they are raised per the Python documentation.
• Remove monitor thread logic from progress, since it is no longer needed
• Update accelerator code to work with new progress design

Closes #1048.

[codecov]

Codecov Report

❌ Patch coverage is 89.34911% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.67%. Comparing base (a5029e9) to head (7c36a1d).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/accel/progress.rs	86.66%	10 Missing ⚠️
src/accel/sparse/consumer.rs	33.33%	6 Missing ⚠️
src/accel/als/explicit.rs	92.30%	1 Missing ⚠️
src/accel/als/implicit.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1050      +/-   ##
==========================================
- Coverage   89.78%   89.67%   -0.12%     
==========================================
  Files         223      223              
  Lines       15497    15476      -21     
==========================================
- Hits        13914    13878      -36     
- Misses       1583     1598      +15     

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