Reduce mutation in the agent state machine

[chkeita]

Summary of the Pull Request

Removing the shared mutable state (&mut self) from the agent state machine. The intent is to make the code easier to reason with.

[codecov-commenter]

Codecov Report

Merging #2710 (11587bb) into main (3a5101b) will decrease coverage by 0.00%.
The diff coverage is 32.96%.

@@            Coverage Diff             @@
##             main    #2710      +/-   ##
==========================================
- Coverage   28.55%   28.55%   -0.01%     
==========================================
  Files         320      320              
  Lines       38050    38108      +58     
==========================================
+ Hits        10866    10881      +15     
- Misses      27184    27227      +43     

Impacted Files	Coverage Δ
src/agent/onefuzz-agent/src/commands.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/config.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/coordinator.rs	5.26% <0.00%> (-0.38%)	⬇️
src/agent/onefuzz-agent/src/debug.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/main.rs	0.42% <0.00%> (ø)
src/agent/onefuzz-agent/src/reboot.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/setup.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/work.rs	10.85% <0.00%> (-0.44%)	⬇️
src/agent/onefuzz-agent/src/worker.rs	57.94% <0.00%> (ø)
src/agent/onefuzz-agent/src/reboot/double.rs	5.00% <6.66%> (-3.34%)	⬇️
... and 8 more

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