fix precisedelta dropping sign of negative timedeltas (fixes #379)

[aDragon0707]

Fixes #379.

precisedelta() silently dropped the sign of negative timedeltas — the output was byte-identical to the positive counterpart (1 hour, 1 minute and 1 second for both -3661 and +3661 seconds).

• Detect a negative value before _date_and_delta, then prefix - on the rendered result.
• Zero stays 0 seconds (no -0).
• Positive inputs are unchanged.

Regression test added (test_precisedelta_negative): seconds, positive control, and minimum_unit="minutes".

tests/test_time.py → 388 passed, 0 failed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.57%. Comparing base (2ad3641) to head (0522fed).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #395   +/-   ##
=======================================
  Coverage   99.56%   99.57%           
=======================================
  Files          12       12           
  Lines         927      938   +11     
=======================================
+ Hits          923      934   +11     
  Misses          4        4           

Flag	Coverage Δ
macos-latest	97.65% <100.00%> (+0.02%)	⬆️
ubuntu-latest	97.65% <100.00%> (+0.02%)	⬆️
windows-latest	95.52% <100.00%> (+0.05%)	⬆️

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[hugovk]

Fixes #379.

If you open this issue, you'll see there's already an open PR for this: #380.

Please check next time, I'm getting so many duplicates that it wastes review time that can be spent elsewhere.