fix: drain closed accumulator window on re-opened key

[vaibhavtiwari33]

Related issues

Related to #3262

Testing

How was this tested (unit/integration/manual)? Include commands, links, or screenshots if applicable.

Special notes for reviewers

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[codecov]

Codecov Report

❌ Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.98%. Comparing base (aa4a5b2) to head (cbc275a).

Files with missing lines	Patch %	Lines
...c/reduce/reducer/unaligned/windower/accumulator.rs	97.95%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3494   +/-   ##
=======================================
  Coverage   82.97%   82.98%           
=======================================
  Files         308      308           
  Lines       79788    79836   +48     
=======================================
+ Hits        66207    66254   +47     
- Misses      13013    13014    +1     
  Partials      568      568           

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