chore: add open-source project files (license, security, CI)

[christiangda]

Rounds out the repository with the standard files expected of a public open-source Go library, mirroring the setup used in slashdevops/httpx.

What's added

• LICENSE — Apache-2.0.
• SECURITY.md — security policy pointing at CodeQL scanning and how to report vulnerabilities.
• .github/workflows/codeql.yml + .github/codeql/codeql-config.yml — CodeQL Advanced code scanning (Go + Actions) on push/PR to main and a weekly schedule.
• .golangci.yaml — golangci-lint v2 configuration.
• DEVELOPMENT_GUIDELINES.md + .github/copilot-instructions.md — contributor/development guidelines.
• .github/FUNDING.yml — funding links.
• .github/dependabot.yml — weekly gomod and github-actions dependency updates.

README

• Removed the Go Report Card badge (the service has been retired). The remaining badges (Go Reference, go.mod version, license, Release) are unchanged.

All existing files were left untouched; go build and go vet pass.

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

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• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.