feat: support go 1.26 and 1.27

[not-matthias]

Adds a version-matched benchmark.go overlay for Go 1.26 (the upstream file is identical in 1.27) and extends the CI test matrix to 1.26.x and 1.27.x.

Closes COD-3356

[codspeed-hq]

Hooray! CodSpeed harness just leveled up!

The base and head of this comparison were measured with different runner settings, so their benchmark values are not directly comparable.

What changed between base and head:

• CodSpeed runner v5 changed how benchmarks are measured (base 4.18.0 → head 5.0.2). View release notes
• CodSpeed runner v5 changed how benchmarks are measured (base 4.18.0 → head 5.1.0). View release notes

Re-run the base with the same settings to get a valid performance comparison.

---

_{Comparing cod-3356-support-go-126-and-127 (93eb80f) with main (e9f4807)}

[greptile-apps]

Greptile Summary

Adds Go 1.26 and 1.27 support by introducing an instrumented Go 1.26 benchmark overlay and selecting it for newer toolchains.

• Extends CI coverage through Go 1.27.
• Adds and documents the Go 1.26 overlay and regeneration patch.
• Updates runtime overlay selection based on the detected Go version.

Confidence Score: 5/5

The PR appears safe to merge with no concrete blocking or non-blocking defects identified.

The new overlay follows the existing instrumentation pattern, version selection routes the intended toolchains to it, and the expanded CI matrix exercises actual overlay-backed benchmark execution.

Important Files Changed

Filename	Overview
go-runner/src/runner/overlay/mod.rs	Selects the new Go 1.26 benchmark overlay for Go 1.26 and later while preserving existing selections for older toolchains.
go-runner/overlay/benchmark1.26.0.go	Adds the Go 1.26 testing benchmark implementation with the established CodSpeed instrumentation lifecycle.
go-runner/overlay/benchmark1.26.0.patch	Records the instrumentation delta from the upstream Go 1.26 benchmark implementation.
.github/workflows/ci.yml	Expands the integration-test matrix to Go 1.26.x and 1.27.x.

_{Reviews (1): Last reviewed commit: 39a9bca | Re-trigger Greptile}

[GuillaumeLagrange]

Olgtm

[GuillaumeLagrange]

Shouldnt we also add 1.27 here?

[GuillaumeLagrange]

If it's just a matter of the patch being the same, wouldnt it be better handled eitehr with a symlink, or a small system that removes the pure coupling between patch file and go version in order for it to be understandable in the future?