v1.6.1

Maintenance release. Bumps the Go toolchain to 1.26.4 and refreshes CI
tooling and pinned action versions. No library source or public API
changes since 1.6.0.

Changed

• Go toolchain bumped to 1.26.4 (go.mod).
• CI govulncheck step refactored.
• Pinned GitHub Actions bumped: actions/checkout,
  golangci/golangci-lint-action, codecov/codecov-action.

Documentation

• Added a WithEventCallback usage example.