Make WindowAggregate::value pass mutable value ref

[nyurik]

Fixes #1394

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (476a02a) 81.33% compared to head (3b70307) 81.35%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1395      +/-   ##
==========================================
+ Coverage   81.33%   81.35%   +0.01%     
==========================================
  Files          49       49              
  Lines       10229    10227       -2     
==========================================
  Hits         8320     8320              
+ Misses       1909     1907       -2     

Files	Coverage Δ
src/functions.rs	87.25% <100.00%> (+0.26%)	⬆️

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[nyurik]

Seems like there is an unrelated Clippy issue. I can submit a PR for auto-checking that, similar to what I have in my crate:

• automatically adds a git-push hook to run cargo clippy && cargo test before pushing (and explains how to skip it)
• use justfile (not required, but convenient) for all sorts of dev life automation

[nyurik]

@gwenn hi, a friendly ping - let me know if anything else is needed here and in other PRs. Thanks!!