Add CodeQL static analysis workflow.

[timmiesmith]

The PR adds CodeQL static code analysis. Static code analysis is one of the best practices for open source repos suggested by the OpenSSF scorecard.

[github-advanced-security]

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[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved blocking issues were identified.

Review effort: Lite
Findings: None

What changed in this PR

Adds a GitHub Actions CodeQL static-analysis workflow for the header-only C++ library.

Changes:

• Runs on pushes, relevant pull requests, and a weekly schedule.
• Configures C/C++ no-build analysis with required permissions.

File	Description
.github/​workflows/​codeql.yml	Defines the CodeQL static-analysis workflow.

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[omalyshe]

LGTM