…ult` and `Dispatchers.IO` (#3562)

* Handle `Dispatchers.IO.limitedParallelism(Int.MAX_VALUE)` case

`LimitedDispatcher.limitedParallelism` returns `this` if requested parallelism is greater or equal
to the own parallelism of the said `LimitedDispatcher`. `UnlimitedIoScheduler` has parallelism effectively set
to `Int.MAX_VALUE`, so `parallelism >= this.parallelism` check folds into `parallelism == Int.MAX_VALUE`.

Before the change `LimitedDispatcher(Int.MAX_VALUE)` was returned. While it does work as expected, any submitted task
goes through its queue and `Int.MAX_VALUE` number of workers. The change allows eliminating the `LimitedDispatcher`
instance and its queue in this extreme case.

* Handle `Dispatchers.Default.limitedParallelism` when requested parallelism >= core pool size (#3442)

`LimitedDispatcher.limitedParallelism` returns `this` if requested parallelism is greater or equal
to the own parallelism of the said `LimitedDispatcher`. `DefaultScheduler` has parallelism effectively set
to `CORE_POOL_SIZE`.

Before the change `LimitedDispatcher(parallelism)` was returned. While it does work as expected, any submitted task
goes through its queue and `parallelism` number of workers. The change allows eliminating the `LimitedDispatcher`
instance and its queue in case the requested parallelism is greater or equal to `CORE_POOL_SIZE`.

Fixes #3442
Added benchmarks on cacheable child serializers

Relates #1918