fix: remove caching on bins

[tlambert03]

@ashesh-0, in playing around with fluors in #18, I found an issue with the caching in bin_events. Namely, the generated bins do depend on em_events, but em_events aren't a part of the cache key... so if you ever calculate bins for a given fluorophore & num-bins with a weird em_events, you never recover from it. For example, if you calculate an off-channel fluorophore (like mCherry detected in the EGFP channel... which will have nearly no events), then forever more you get weird bins for mCherry.
I don't think it's a performance bottle neck yet, so this PR just removes the caching

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.83%. Comparing base (96cf3cf) to head (aa9f900).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
- Coverage   85.86%   85.83%   -0.04%     
==========================================
  Files          50       49       -1     
  Lines        2702     2696       -6     
==========================================
- Hits         2320     2314       -6     
  Misses        382      382              

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