Add check_spike_times_without_nans

[h-mayorquin]

Spike times are physical event timestamps representing when action potentials occurred. A spike either happened at a specific time or it didn't, so NaN is never a meaningful value. NaN in spike times typically indicates a conversion bug or array padding that was not cleaned up before writing to NWB.

Unlike other spike time checks that sample the first N elements, this check scans the full array because NaN values can appear at any position in the data.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.12%. Comparing base (60bfe7f) to head (3144a11).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #689      +/-   ##
==========================================
+ Coverage   79.87%   83.12%   +3.25%     
==========================================
  Files          48       48              
  Lines        1873     1885      +12     
==========================================
+ Hits         1496     1567      +71     
+ Misses        377      318      -59     

Files with missing lines	Coverage Δ
src/nwbinspector/checks/__init__.py	100.00% <ø> (ø)
src/nwbinspector/checks/_ecephys.py	94.35% <100.00%> (+0.41%)	⬆️

... and 5 files with indirect coverage changes

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[h-mayorquin]

@bendichter was this added accidentally?