[TS] Allow `ReadonlyArray` everywhere we have `Array`

[dawsbot]

Currently there is an error if you want to pass in a ReadonlyArray to a constructor like "new FallthroughProvider(bscRpcs)". In these situations we should also allow readonly arrays. This does not change any JS, only TS

Also find any other relevant places in the codebase this would be an issue for library consumers