[MaurizioSodano]

Adds Dart (and Flutter) to crapper.

• .dart files are scored: top-level functions, methods of classes, mixins, extensions, extension types and enums, getters (size), setters (size=), operators (operator +) and factory constructors. Generative constructors, abstract and external members are not entries; local functions and closures count toward the function that holds them.
• Complexity counts if, for, while, do, catch/on, ?:, each switch case, &&, ||, ??, ?. and collection if/for.
• Namespace is the package name from pubspec.yaml plus the path under lib/.
• Coverage is LCOV: flutter test --coverage when the package depends on sdk: flutter, otherwise dart test, once per package. Relative SF: paths are made absolute. --use-existing-coverage also reads each package's coverage/lcov.info.
• Generated files (*.g.dart, *.freezed.dart, *.mocks.dart, ...), .dart_tool, test/, integration_test/ and *_test.dart are skipped.
• Includes a fix for _coverage_report raising ValueError when a package is outside --root.

Tested on a Flutter monorepo (680 Dart files, 3,786 functions, no parse errors, 4.8 s without coverage) and with a real flutter test --coverage run.

Tests: tests/test_dart.py, tests/test_dart_coverage.py; suite 169 pass. The one failure, test_project_snapshot_is_readable_as_crap4clj_edn, and the parse_args CRAP 16 are on master already.

Sibling PRs: unclebob/dryer and unclebob/mutator. mutator imports crapper.dart_coverage, so merge this one first.

https://claude.ai/code/session_01L2LePAtan3pdyUWbr64gpS