feat: significantly reduce allocations

[costela]

This PR sacrifices a bit of readibility for significant less allocations:

goos: linux
goarch: amd64
pkg: github.com/exaring/ja4plus
cpu: AMD Ryzen 7 7840U w/ Radeon  780M Graphics     
       │  old.bench  │              new.bench              │
       │   sec/op    │   sec/op     vs base                │
JA4-16   684.6n ± 1%   207.8n ± 1%  -69.65% (p=0.000 n=10)

       │  old.bench  │             new.bench              │
       │    B/op     │    B/op     vs base                │
JA4-16   240.00 ± 0%   48.00 ± 0%  -80.00% (p=0.000 n=10)

       │  old.bench  │             new.bench              │
       │  allocs/op  │ allocs/op   vs base                │
JA4-16   15.000 ± 0%   1.000 ± 0%  -93.33% (p=0.000 n=10)

[Copilot]

Pull Request Overview

This PR optimizes the JA4 fingerprinting algorithm to significantly reduce memory allocations while maintaining the same functionality. The changes replace string concatenation and fmt.Sprintf calls with manual byte buffer manipulation and custom hex encoding functions.

Key changes:

• Replace slice operations and string formatting with manual loops and byte operations
• Introduce custom helper functions for hex encoding and digit formatting
• Change hash functions to return fixed-size byte arrays instead of slices

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

File	Description
ja4plus.go	Core optimization replacing string operations with byte buffer manipulation and custom encoding functions
ja4plus_test.go	Update test to work with new hash function signature returning byte array
examples_test.go	Update expected output and add comment about Go version differences
.github/workflows/ci.yml	Add Go 1.25 to test matrix

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 5 changed files in this pull request and generated no new comments.

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