perf(collections): optimize deepMerge

[tomas-zijdemans]

Made deepMerge faster by:

• Skipping unnecessary work when objects have no Symbol keys (most objects)
• Merging Sets and Maps without creating temporary arrays

Perf gains depend on the use case, but I see a overall 15-20% improvement. I can't find any regressions.

Also:

• Removed the dependency on filterInPlace
• Cached default options as a constant (no perf impact)
• Added more tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.30%. Comparing base (6b93b78) to head (05d14c7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6948      +/-   ##
==========================================
+ Coverage   94.28%   94.30%   +0.01%     
==========================================
  Files         584      584              
  Lines       43186    43195       +9     
  Branches     6933     6936       +3     
==========================================
+ Hits        40720    40734      +14     
+ Misses       2413     2409       -4     
+ Partials       53       52       -1     

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