[CQ] Unnecessary code cleanup

[pq]

Addressed/removed unnecessary code in the form of:

• redundant suppressions
• redundant throws
• redundant casts
• unused imports
• redundant toString(), substring(..) calls
• unnecessary default branches
• explicit types where <> will do
• stream API call chains where toList() is enough

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 the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• 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.