fix(deps): update dependency source_gen to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
source_gen (source)	dependencies	major	^1.2.2 → 4.2.0

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Release Notes

dart-lang/source_gen (source_gen)

v4.2.0

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• Add header configuration to CombiningBuilder.

v4.1.2

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• Allow analyzer: '>=8.1.1 <11.0.0'.

v4.1.1

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• Allow analyzer: '>=8.1.1 <10.0.0'.

v4.1.0

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• Add TypeChecker.typeNamedLiterally. It's like TypeChecker.typeNamed,
  but takes a String instead of a Type.

v4.0.2

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• Bug fix: fix possible null pointer exception in TypeChecker.typeNamed on
  invalid code.

v4.0.1

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• Require analyzer: '>=8.1.1 <9.0.0'.
• Allow build: '>=3.0.0 <5.0.0'.

v4.0.0

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• Breaking Change: remove TypeChecker.fromRuntime, use
  TypeChecker.typeNamed instead. This removes all use of dart:mirror, so
  builders using source_gen can be AOT compiled for better performance.
• Keep // GENERATED FILE comments on the first line.

v3.1.0

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• Prepare to stop using dart:mirrors: deprecate TypeChecker.fromRuntime.
  It will be removed in version 4.0.0. Add TypeChecker.typeNamed which is
  the recommended replacement.
• Prepare to stop using dart:mirrors: add inPackage and inSdk parameters
  to GenerateForAnnotation. These will start being used in version 4.0.0
  when it switches to TypeChecker.typeNamed.
• InvalidGenerationSource support for Fragment, ElementDirective and
  Annotatable.
• Allow analyzer: '>=7.4.0 <9.0.0'.

v3.0.0

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• Breaking Change: use the new element2 APIs in analyzer. Builders that
  do resolution need to switch to the new API, see
  https://github.com/dart-lang/sdk/blob/main/pkg/analyzer/doc/element_model_migration_guide.md.
  For questions please use https://github.com/dart-lang/build/discussions.
• Breaking Change: annotations are now reported separately for elements
  and directives. If you use TypeChecker().annotatedWith(), see also
  the new TypeChecker().libraryDirectivesAnnotatedWith(). If you use
  GeneratorForAnnotation see the new generateForAnnotatedDirective.
• Require build: ^3.0.0
• Updated the minimum package versions for a number of dependencies.
• Require Dart 3.7.0
• Update the GeneratorForAnnotation optimization to skip files with well known
  annotation names such as override, Deprecated, and pragma.

v2.0.0

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• Breaking Change: Change formatOutput function to accept a language
  version parameter.
• Formatting Change: Generated code will no longer apply any fixes by
  default (previously it would apply the single cascades statements fix). The
  new formatter does not support applying fixes.
• Document deduplication behavior for the output of
  GeneratorForAnnotation.generateForAnnotatedElement.
• Support all the glob quotes.
• Require analyzer: '>=6.9.0 <8.0.0'
• Support the latest package:dart_style
• LibraryBuilder, PartBuilder, and SharedPartBuilder now take an optional
  writeDescriptions boolean. When set to false, headers and generator
  descriptions for the files will not be included in the builder output.
• Include //dart format width=80 comments in files generated by a
  LibraryBuilder or PartBuilder and formatted with the default callback.
• Require Dart 3.6.0

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