Prepare universal_ffi 1.5.1 trusted publishing

[vm75]

Release preparation

• Removed the root and example dependency_overrides entries for wasm_ffi; dependency resolution now uses hosted wasm_ffi 2.4.0 from pub.dev.
• Removed sibling checkout and local version rewriting from CI and publishing.
• Replaced push-to-main/token publishing with the official tag-based OIDC reusable workflow for v{{version}}. No PUB_TOKEN is required.
• Kept package version at 1.5.1 and dependency at wasm_ffi: ^2.4.0.

Validation

• Dart 3.10.8 / Flutter 3.38.9
• dart pub get
• dart format --output=none --set-exit-if-changed .
• dart analyze
• dart test
• dart pub publish --dry-run (0 warnings)
• Flutter plugin and example flutter analyze
• flutter build web
• flutter build web --wasm

Manual release prerequisite

Configure pub.dev trusted publishing for repository vm75/universal_ffi with tag pattern v{{version}} before creating v1.5.1. After merge, verify main CI is green, create the tag on the merged main commit, inspect the publish Action, and confirm pub.dev lists universal_ffi 1.5.1.