Particles.fuse reports negligible weights after successful reweighting

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## Summary

`Particles.fuse(verbose=True)` reports "All weights are negligible" when `reweight()` succeeds.

## Problem

`Particles.reweight()` documents and returns `True` for success and `False` when all particle weights are negligible. `Particles.fuse()` currently checks:

```python
if status > 0 and verbose:
print("All weights are negligible in Particles class")
```

Because `True > 0`, the warning is emitted on successful reweighting and suppressed on the failure condition it is intended to report.

An existing regression test also encodes the inverted behaviour by monkeypatching `reweight()` to return `True` and asserting that the warning is printed.

## Expected behaviour

The warning should be emitted only when `reweight()` returns `False` and `verbose=True`.

## Proposed change

- Change the condition to `if not status and verbose:`.
- Update the regression test to assert no warning on success and a warning on failure.

Start with Particles.fuse() and its call to reweight(), then locate the existing regression test that monkeypatches reweight(). Run that test first; completion means the warning appears only for a False status with verbose=True, while successful reweighting produces no warning.

Written by the indexing model from the issue text.