* swift 6 support for NSE and concurrency safe implementations for it
* enforcing required Sendable conformance for swift 6 migration in NSE
* use Mutex to access the string builder cache
* use an async stream to update timeline items diffs
* fix for Sendable appHooks
* Fix various small errors when running in the Swift 6 language mode
* Make the `TargetConfiguration` run on the main actor.
* Fixed a comment
* Add a comment as to why we can't make the whole NSE a main actor.
* Fix the unit tests
* Fix `blankLinesAtStartOfScope` swiftformat error.