chore: upgrade Go toolchain 1.25.4 → 1.27.0

[kolkov]

Summary

Upgrade Go toolchain from 1.25.4 to 1.27.0 to benefit from three compiler optimizations:

• Known-bits dataflow pass — tracks provable 0/1 bits, folds redundant ops. May eliminate DFA bounds checks on ft[offset]
• Loop-invariant code motion (LICM) — hoists invariants out of loops. 10.17% improvement on regexp/syntax benchmarks (same loop type as our DFA/NFA)
• Switch-to-lookup table — dense switch→table compilation. Benefits our 13-way strategy dispatch

Also: size-specialized malloc for <80 byte objects, Green Tea GC (old GC removed).

Zero breaking changes. All tests pass. Assembly files fully compatible.

Test plan

• go build ./... — clean
• go test ./... — all 11 packages pass
• go vet ./... — clean
• CI: tests on 3 OS (ubuntu, macos, windows)
• CI: benchmark comparison vs main (Go 1.25.4)
• regex-bench: full comparison on AMD EPYC (Go+Rust)

[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 #165

Summary: geomean 76.07n 76.19n +0.16%

⚠️ Potential regressions detected:

geomean                    76.07n         76.19n        +0.16%
geomean                               ³                +0.00%               ³
geomean                               ³                +0.00%               ³
geomean              32.32n         32.33n        +0.02%
geomean                         ³                +0.00%               ³
geomean                         ³                +0.00%               ³
AhoCorasickVsStdlib/stdlib_Find-4                       196.3µ ± ∞ ¹      197.8µ ± ∞ ¹      +0.78% (p=0.016 n=5)
DNA_SizeScaling/64KB-4                                  322.5µ ± ∞ ¹      324.0µ ± ∞ ¹      +0.49% (p=0.008 n=5)
LangArenaLogParser/post_requests-4                      860.1µ ± ∞ ¹      860.9µ ± ∞ ¹      +0.09% (p=0.032 n=5)
LangArenaLogParserStdlib/errors-4                       9.900m ± ∞ ¹     10.048m ± ∞ ¹      +1.50% (p=0.008 n=5)

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