feat: bump go-runner to 1.2.1

[adriencaccia]

Bump the default codspeed-go runner to 1.2.1 and pin its installer SHA-256.

This updates DEFAULT_GO_RUNNER_VERSION and adds the matching
<version> <sha256> row to the GO_RUNNER_INSTALLER_SHA256S table in
go.sh. The pinned hash is verified by GITHUB_ACTIONS=true cargo test all_pinned, which passed locally.

Also documents the two-location pinning setup (src/binary_pins.rs and the
go-runner table) in CONTRIBUTING.md, and the test-driven workflow for getting
a new hash from the verification-test failure rather than computing it by hand.

Refs rather than Closes: this PR is the prerequisite bump — the 4.18.1
runner release (the cargo release tag) is the follow-up step that resolves the
issue.

Refs COD-2990

[greptile-apps]

Greptile Summary

Bumps the default codspeed-go runner to 1.2.1 by adding a new <version> <sha256> row to GO_RUNNER_INSTALLER_SHA256S in go.sh and updating DEFAULT_GO_RUNNER_VERSION. The companion CONTRIBUTING.md update documents the two-location pinning setup (src/binary_pins.rs and the go-runner table) and the test-driven workflow for deriving new hashes.

• go.sh: appends 1.2.1 5c90675148a23fd550681033b5589b39b8e66a8ea372d27befd580be0cc535f4 to the SHA-256 table and sets DEFAULT_GO_RUNNER_VERSION="1.2.1".
• CONTRIBUTING.md: replaces the single-location hash doc with a two-section explanation covering both src/binary_pins.rs and go.sh, and introduces the placeholder-hash / test-failure workflow for obtaining correct hashes.

Confidence Score: 5/5

Safe to merge — the change is a two-line data update (new table row + default version bump) with no logic modifications, and the hash was validated by the all_pinned test suite.

The go.sh change only appends a row to the SHA-256 lookup table and updates the default pointer; the verification path (lookup → download → hash comparison → execute) is unchanged. The 64-character hash is well-formed, the PR description confirms the test passed locally, and CI runs the same test. The CONTRIBUTING.md edits are purely documentation.

No files require special attention.

Important Files Changed

Filename	Overview
src/executor/helpers/introspected_golang/go.sh	Adds 1.2.1 row to the GO_RUNNER_INSTALLER_SHA256S table (64-char SHA-256) and bumps DEFAULT_GO_RUNNER_VERSION; no logic changes.
CONTRIBUTING.md	Expands the "Pinned binary hashes" section to document both pin locations and the test-driven hash workflow; no code impact.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[go.sh invoked with 'test'] --> B{codspeed-go-runner installed?}
    B -- Yes --> E[Run go-runner]
    B -- No --> C[Read CODSPEED_GO_RUNNER_VERSION\nor DEFAULT_GO_RUNNER_VERSION=1.2.1]
    C --> D[get_go_runner_installer_sha256\nlookup in GO_RUNNER_INSTALLER_SHA256S table]
    D --> F[curl download installer]
    F --> G[sha256_file verify against pinned hash]
    G -- mismatch --> H[exit 1 ERROR]
    G -- match --> I[bash installer --quiet]
    I --> E

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[go.sh invoked with 'test'] --> B{codspeed-go-runner installed?}
    B -- Yes --> E[Run go-runner]
    B -- No --> C[Read CODSPEED_GO_RUNNER_VERSION\nor DEFAULT_GO_RUNNER_VERSION=1.2.1]
    C --> D[get_go_runner_installer_sha256\nlookup in GO_RUNNER_INSTALLER_SHA256S table]
    D --> F[curl download installer]
    F --> G[sha256_file verify against pinned hash]
    G -- mismatch --> H[exit 1 ERROR]
    G -- match --> I[bash installer --quiet]
    I --> E

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_{Reviews (1): Last reviewed commit: "docs: document go-runner hash table and ..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks

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_{Comparing cod-2990-release-runner (4d094a3) with main (618f1b1)}