feat: add SARIF format

[jakeva]

Added --format sarif which outputs a SARIF 2.1.0 document. Each violation becomes a result with ruleId, level: "error", the message, and a physicalLocation pointing to the file.

Also added a scan job in CI that builds spinlint, runs it against testdata/*.json, and uploads the SARIF to GitHub Code Scanning via codeql-action/upload-sarif.

[github-advanced-security]

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