Performance optimizations suggested by Claude.ai

[jlblancoc]

Benchmark results: time gains in both kd-tree build and query:

• Observe new optional macro NANOFLANN_NODE_ALIGNMENT, defaulting to 16 bytes.
• middleSplit_(): Single-pass min/max computation for candidate dimensions.
• planeSplit(): Dutch National Flag algorithm for three-way partitioning

[codecov]

Codecov Report

❌ Patch coverage is 86.40777% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.07%. Comparing base (ce38bbd) to head (4effd9d).

Files with missing lines	Patch %	Lines
include/nanoflann.hpp	86.40%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #279      +/-   ##
==========================================
- Coverage   84.25%   84.07%   -0.19%     
==========================================
  Files           1        1              
  Lines         705      722      +17     
  Branches      130      126       -4     
==========================================
+ Hits          594      607      +13     
- Misses        111      115       +4     

Files with missing lines	Coverage Δ
include/nanoflann.hpp	84.07% <86.40%> (-0.19%)	⬇️

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