refactor(arbiter-engine): agent-behavior flow

[Autoparallel]

Give an overview of the tasks completed
This PR adds the ability for the sync() stage of a Behavior to receive the client and messager from the agent the behavior is attached to. It should then be recommended to users to make these fields optional in their behaviors at some point down the road, but we are not done with this design yet. There could be better ways to address this problem, but I'll take this for now.

Link to issue(s) that this PR closes
Closes #819

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (c1ae130) 55.80% compared to head (d31821a) 55.08%.
Report is 9 commits behind head on main.

Files	Patch %	Lines
arbiter-engine/src/machine.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #820      +/-   ##
==========================================
- Coverage   55.80%   55.08%   -0.72%     
==========================================
  Files          37       35       -2     
  Lines        7643     7488     -155     
==========================================
- Hits         4265     4125     -140     
+ Misses       3378     3363      -15     

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[0xJepsen]

nice this seems like a clear improvement on the prior version.