chore: release v2.21.1

[tickernelz]

Release

Patch release for the cross-platform package-smoke and Turso/libSQL lifecycle fixes merged in #200.

Included fixes

• build artifacts before clean-runner tests/package smoke
• serialize Turso close/open races and release Windows libSQL handles before file mutations
• bounded Windows lock retries for migration/file cleanup paths
• stable Windows Git worktree path identity
• isolated libSQL vector smoke cleanup
• replace retired macos-13 with macos-15-intel
• preserve the package's optional onnxruntime-node override in packed-consumer smoke tests

Verification

• bun install --frozen-lockfile
• bun run typecheck
• bun run build
• bun test — 269 pass, 0 fail, 591 assertions
• npm pack --dry-run --ignore-scripts --json — version 2.21.1, 200 files, manifest and dist/plugin.js present
• ci: build artifacts before package smoke tests #200 final matrix: Ubuntu, Windows, macOS ARM, and macOS Intel all green

Version-only release commit; tag v2.21.1 will be created from the merged release commit after this PR is green.