In prep to support a distributed/redis scheduler, prepare the state
interface to no longer take mutable references.

This is a partial PR and should be landed immediately with followup PRs
that will remove many of the locking in the SimpleScheduler.

towards: TraceMachina#359

Worker logic should not be visible to StateManager just yet. In the
future this will likely change, but for this phase of the refactor
SimpleScheduler should own all information about workers.

towards: TraceMachina#359

Moves the logic on when the matching enginge trigger gets run to
under the workers struct where easy. This splits the logic of
when a task is changed and matching engine needs to run and when
a task gets run and the matching engine needs to be run.

towards: TraceMachina#359

This is a complete rewrite of way the scheduler works internally.
No changes should be externally visible.

Introduces various code quality improvements to scheduler-v2
which allow bazel test to pass.

Co-authored-by: Zach Birenbaum <zacharyobirenbaum@gmail.com>

…raceMachina#1091)

This will enable the underlying scheduler to intercept the Drop
call allowing easier cleanups of actively listened actions.

ActionStateResult is now wired up to ActionListener allowing
it to be notified of Drop calls. This will be used to do client
operation id cleanups.

Worker stream now properly terminated on action complete.

…ina#1107)

StateManager will now properly remove items from the maps if the
client disconnects after a set amount of time. Currently these
values are hard codded, but will be easy to transition them to
use config variables once we design it out.

In order to make the refactor easier we are removing all metrics.

We will add them back in later.

Removes unused proto field in worker api.