feat: log serendipity message before additional drop

[midgleyc]

Make it easier to tell when a drop came from serendipity.

[codecov]

Codecov Report

Merging #1901 (ea3f6b2) into main (5710869) will increase coverage by 0.00%.
The diff coverage is 28.57%.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1901   +/-   ##
=========================================
  Coverage     36.37%   36.37%           
- Complexity    18826    18827    +1     
=========================================
  Files          1083     1083           
  Lines        166580   166587    +7     
  Branches      35384    35388    +4     
=========================================
+ Hits          60593    60603   +10     
+ Misses        96110    96106    -4     
- Partials       9877     9878    +1     

Files Changed	Coverage Δ
...et/sourceforge/kolmafia/objectpool/EffectPool.java	100.00% <ø> (ø)
...net/sourceforge/kolmafia/request/FightRequest.java	34.29% <28.57%> (-0.01%)	⬇️

... and 7 files with indirect coverage changes

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