feat: add class-model helpers for code generators (1.4.0) - #78

…uilder (#102)

Adopts the shared constructor, property-annotation, enum, and
nullability helpers published in [`package:source_helper`
`1.4.0`](google/source_helper.dart#78).

- Adds `source_helper: ^1.4.0` to `pkgs/codable_builder/pubspec.yaml`.
- Replaces local `constructorByName`, `firstAnnotationOnProperty`,
`DartType.enumConstants`, and `DartType.isNullableType` helpers across
`model_visitor.dart`, `type_helper.dart`, `encoder_helper.dart`, and
`decoder_helper.dart`.
- Inherits `@CodableKey` and `@CodableTuple` annotations from overridden
superclass and superinterface properties (`firstAnnotationOnProperty`).

… ^1.4.0 (#13337)

Fixes flutter/flutter#194817

Adopts shared analyzer helpers published in [`package:source_helper` `1.4.0`](google/source_helper.dart#78) to replace local copies in `go_router_builder`:

- Bumps `source_helper` constraint to `^1.4.0` and `go_router_builder` to `4.5.2`.
- Replaces local `ExecutableElement.qualifiedName`, `withoutNullability` / `_isNullableType`, and `isEnumConstant` filtering across `type_helpers.dart`, `route_config.dart`, and `go_router_generator.dart` with `ExecutableElement.qualifiedName`, `DartType.toStringNonNullable()`, and `DartType.enumConstants` from `package:source_helper/source_helper.dart`.

Pure internal deduplication; generated code is unchanged (`tool/run_tests.dart` and `example/test/ensure_build_test.dart` pass with zero diffs).

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Adds an opt-in `--rev-deps` flag to `kscripts pr-check` that validates
touched publishable packages against already-published downstream
consumers on `pub.dev` before a non-major release.

### Why
- Isolated API diffing tools (`dart_apitool`, `api_summary`) classify
adding public top-level symbols or `extension` members as
backwards-compatible minor changes, even when downstream consumers on
`pub.dev` already import the package entrypoint without `show` and
declare colliding extension members
(`ambiguous_extension_member_access`) or top-level helpers
(`ambiguous_import`), as occurred in
google/source_helper.dart#78 (`1.4.0`).
- Validating against downstream `HEAD` branches misses these collisions
when donor helpers have already been deleted on the consumer's feature
branch.

### Non-Obvious Callouts
- Default `pr-check` runs make zero network calls and record `Skipped:
rev-deps:<pkg> (pass --rev-deps to run)` when a publishable package
modifies `lib/` in a non-major release
(`VersionConstraint.compatibleWith(baseRelease).allows(targetRelease)`).
- When `--rev-deps` is passed, `pr-check` queries `pub.dev`
(`dependency:<pkg>` and `dependency:<pkg> publisher:kevmoo.com`) plus
`~/.pub-cache/hosted/pub.dev`, unpacks each compatible consumer via
`dart pub unpack <consumer> --no-resolve`, strips
`analysis_options.yaml`, `resolution`, `workspace`, and
`dev_dependencies` via `YamlEditor`, writes `pubspec_overrides.yaml`
pointing `<pkg>` to the local checkout, and runs `dart pub get` + `dart
analyze lib`.

### Verification
- Verified against `source_helper` `1.4.0`: `[email protected]`
fails `dart analyze lib` with `11` real compile errors
(`ambiguous_import` on `constructorByName` / `createSortedFieldSet` and
`ambiguous_extension_member_access` on `toStringNonNullable` /
`qualifiedName`), while `[email protected]`, `[email protected]`,
and `[email protected]` pass cleanly.