Apply more strict typescript around the codebase (#2778)
* Apply more strict typescript around the codebase
* Fix tests
* Revert strict mode commit
* Iterate strict
* Iterate
* Iterate strict
* Iterate
* Fix tests
* Iterate
* Iterate strict
* Add tests
* Iterate
* Iterate
* Fix tests
* Fix tests
* Strict types be strict
* Fix types
* detectOpenHandles
* Strict
* Fix client not stopping
* Add sync peeking tests
* Make test happier
* More strict
* Iterate
* Stabilise
* Moar strictness
* Improve coverage
* Fix types
* Fix types
* Improve types further
* Fix types
* Improve typing of NamespacedValue
* Fix types
