docs: update benchmark results to v0.12.6

[kolkov]

Update README.md and ROADMAP.md benchmark tables with v0.12.6 results from regex-bench CI (AMD EPYC). Add vs Rust column.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[github-actions]

Benchmark Comparison

Comparing main → PR #131

Summary: geomean 124.1n 121.6n -1.99%

⚠️ Potential regressions detected:

geomean                               ³                +0.00%               ³
geomean                               ³                +0.00%               ³
geomean                         ³                +0.00%               ³
geomean                         ³                +0.00%               ³
AhoCorasickManyPatterns/coregex_10_patterns-4           58.40n ± ∞ ¹    60.48n ± ∞ ¹    +3.56% (p=0.008 n=5)
AhoCorasickManyPatterns/coregex_25_patterns-4           72.47n ± ∞ ¹    74.51n ± ∞ ¹    +2.81% (p=0.032 n=5)
AhoCorasickManyPatterns/stdlib_25_patterns-4            149.3n ± ∞ ¹    151.0n ± ∞ ¹    +1.14% (p=0.016 n=5)
ASCIIOptimization_Issue79/medium_WithASCII-4            620.2n ± ∞ ¹    630.2n ± ∞ ¹    +1.61% (p=0.008 n=5)
DNA_VsStdlib/stdlib/dna_4-4                             57.91m ± ∞ ¹    85.67m ± ∞ ¹   +47.92% (p=0.008 n=5)
AnchoredAlt_ManyBranches_Stdlib/GET-4                   83.10n ± ∞ ¹    85.69n ± ∞ ¹    +3.12% (p=0.032 n=5)

Full results available in workflow artifacts. CI runners have ~10-20% variance.
For accurate benchmarks, run locally: ./scripts/bench.sh --compare