Code cleanup and warning checkup

[qsdigor]

While working on implementation/version-2 I noticed many deprecated methods, lousy formatting, and other warnings.

Running lint revealed 133 errors, 2.297 warnings, 56 week-warnings, and 1.393 typos. While a lot of them are not valid warnings a lot of them are and should be addressed.

We should run code formatting and optimize imports so everything is tidy.

┆Issue is synchronized with this Jira Task by Unito

[sync-by-unito[bot]]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2866

[QuintinWillison]

Work on this issue will need to include adding these lint checks to CI in our check workflow. I understand from @qsdigor that the command he's using locally (which we don't currently run in CI) is ./gradlew lint or in IntelliJ "toolbar -> code -> inspect code -> whole project -> ok".