[go_router_builder] Support nested parentheses, groups, and lookaround assertions in path parameters

[MaximeRougieux]

• Fixes [go_router_builder] Support nested parentheses, groups, and lookaround assertions in path parameters (Follow up on https://github.com/flutter/packages/pull/12571) flutter#192300

See #12571 for details about the changes

Pre-Review Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools.
• I read the [Tree Hygiene] page, which explains my responsibilities.
• I read and followed the [relevant style guides] and ran [the auto-formatter].
• I signed the [CLA].
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I [linked to at least one issue that this PR fixes] in the description above.
• I followed [the version and CHANGELOG instructions], using [semantic versioning] and the [repository CHANGELOG style], or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which [test exemption] this PR falls under[^1].
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request refactors path parameter parsing in path_utils.dart to support nested parentheses, grouping constructs, and lookahead assertions by replacing the previous regular expression with a custom scanning mechanism. It also adds corresponding unit tests and bumps the package version to 4.4.1. Feedback is provided regarding a missing import for package:collection/collection.dart which is required for the firstOrNull extension getter.

[gemini-code-assist]

The firstOrNull extension getter is used on line 33, but package:collection/collection.dart is not imported in this file. This will cause a compile-time error. Please add the import at the top of the file.

Suggested change

	final RegExp _parameterNameRegExp = RegExp(r':(\w+)');
	import 'package:collection/collection.dart';
	final RegExp _parameterNameRegExp = RegExp(r':(\w+)');