Fix Particles fuse negligible-weight status

[sylvesterkaczmarek]

Summary

Fix the inverted verbose-status check in Particles.fuse().

Changes

• Emit the negligible-weight warning only when reweight() reports failure.
• Update the existing regression test to verify that successful reweighting is silent.
• Add the corresponding failure-path assertion so the warning remains covered.

Testing

• python3 -m py_compile ssapy/particles.py tests/test_particles.py
• git diff --check

The local environment does not have the full SSAPy pytest dependency stack installed, so repository CI will provide the full test run.

Fixes #141

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.39%. Comparing base (a895a5b) to head (c743175).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #142   +/-   ##
=======================================
  Coverage   97.39%   97.39%           
=======================================
  Files          17       17           
  Lines        5820     5820           
=======================================
  Hits         5668     5668           
  Misses        152      152           

Flag	Coverage Δ
unittests	97.39% <100.00%> (ø)

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Files with missing lines	Coverage Δ
ssapy/particles.py	100.00% <100.00%> (ø)

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[sylvesterkaczmarek]

Thanks for merging this one as well. Much appreciated, and I’m looking forward to contributing more to SSAPy.