Checker: Make YAML format plugin specifier more verbose
Checker: Delegate json packing/unpacking to Rules class
Checker: Remove ability to load plugins manually.

* Plugins are exclusively detected by the registry, and so there is no
  point in filtering them via user input.

* Remove `dry_run` argument from the Checker's API.
Checker: Preliminary support for batch plugins

* Add properties that expose whether a rule is bound to a plugin that is
  "batch" or "simple".

* Spawn nested workflows for "batch" plugins and save the output of
  their pre- function to be passed to the `check_record` one.
Checker: Intersections with intbitset `trailing_bits`

* Utilize intbitset's `trailing_bits` to avoid adding extra logic when
  dealing with `ALL`.