[go_router] improve coverage

[Ascenio]

Before	After

This PR adds new tests, reaching code paths not previously covered as pointed by a coverage report.
Closes #99286

No CHANGELOG change: because it doesn't affect the package's users.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• 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 listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[chunhtai]

Also I have a massive lint update to the package #1017

I would prefer to land it before this pr to avoid adding more tech debt on top of go_router

[chunhtai]

Code looks good. Can you remove the src sub folder? Let's follow the folder structure of other packages. The folder test/ maps to lib/src directly, so you don't need to create a src fold in test folder.

[chunhtai]

Some tests seemed to be gone?

[chunhtai]

LGTM

[Ascenio]

Some tests seemed to be gone?

Technical Difficulties 🤣

[chunhtai]

@Ascenio it looks like there is a conflict?

[chunhtai]

the build fails

�[36m[0:00] Running for go_router...�[0m
3.0.4 -> 3.0.5
�[31m When bumping the version for release, the NEXT section should be incorporated into the new version's release notes.�[0m

[johnpryan]

I think most of my comments can be addressed as a follow-up. I can file issues if they're out of scope for this PR.