chore: exclude generated build files from analysis

[rubensdemelo]

Motivation

• Prevent the Dart analyzer from scanning generated build/ output which causes Flutter to rewrite analysis_options.yaml during verification.
• Make CI and local verification deterministic by excluding generated artifacts from linting and analysis inputs.
• The initial verification appeared to “fail” because dart/flutter were not on the shell PATH, so the environment needed /opt/flutter/bin available to run the checks.

Description

• Add an analyzer: block with `exclude:
  • build/**toanalysis_options.yaml` to keep generated files out of analysis inputs.
• Reverted incidental changes to generated files (pubspec.lock, example/pubspec.lock, example/ios/Flutter/flutter_export_environment.sh, and coverage/lcov.info) so the verification only modifies the intended analyzer configuration.
• Ran verification commands with PATH=/opt/flutter/bin:$PATH so the installed Flutter at /opt/flutter is used for analysis and tests.

Testing

• Ran dart format --set-exit-if-changed . which completed with 78 files checked and no changes and exited successfully.
• Ran flutter analyze which reported "No issues found!" and exited successfully.
• Ran flutter test --coverage which executed the package test suite and reported "All tests passed!" (273 tests) and exited successfully.
• Ran (cd example && flutter test) which executed the example app tests and reported "All tests passed!" (7 tests) and exited successfully.

---

Codex Task