Add ensureParamsCapacity helper to tree.go

[miladev95]

Introduces ensureParamsCapacity(params *Params, needed int) to centralize Params preallocation and adds a short doc comment in tree.go. Internal-only refactor; no API or behavior changes.

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.89%. Comparing base (3dc1cd6) to head (38c2430).
⚠️ Report is 224 commits behind head on master.

Files with missing lines	Patch %	Lines
tree.go	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4463      +/-   ##
==========================================
- Coverage   99.21%   98.89%   -0.33%     
==========================================
  Files          42       44       +2     
  Lines        3182     2977     -205     
==========================================
- Hits         3157     2944     -213     
- Misses         17       20       +3     
- Partials        8       13       +5     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.81% <77.77%> (?)
-tags go_json	98.74% <77.77%> (?)
-tags nomsgpack	98.80% <77.77%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.24	98.89% <77.77%> (?)
go-1.25	98.82% <77.77%> (?)
macos-latest	98.89% <77.77%> (-0.33%)	⬇️
ubuntu-latest	98.82% <77.77%> (-0.40%)	⬇️

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