feat(driver): Turn get_value into an asynchronous step within the state machine

[romac]

When a new round starts and we are the proposer, this PR allows the consensus engine to both schedule a propose timeout and ask the context for a value to propose. Either the timeout or the value to propose can then be fed back into the driver asynchronously as an input event.

TODO

• Adapt Quint specification spec: Sync between driver/consensus and code #81
• Remove the value to propose from RoundEvent::NewRoundProposer
• Add a new input event to both the driver and the round state machine: ProposeValue(Cox::Value) to feed them a value to propose
• Add a new output message to both the round state machine and the driver: GetValueAndScheduleTimeout(Round, Timeout) to ask the context for a value to be asynchronously fed back into the driver via the new ProposeValue event
• In the driver, when a new round starts and we are the proposer, send NewRoundProposer (now without a value) to the round state machine and emit the resulting message (ie. the new GetValueAndScheduleTimeout message)
• Remove Env::get_value
• Remove Error::NoValueToPropose
• Update tests

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (2a7862b) 87.44% compared to head (1822913) 87.16%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
Code/round/src/state_machine.rs	74.00%	13 Missing ⚠️
Code/driver/src/driver.rs	86.84%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   87.44%   87.16%   -0.28%     
==========================================
  Files          30       29       -1     
  Lines        1346     1371      +25     
==========================================
+ Hits         1177     1195      +18     
- Misses        169      176       +7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ancazamfir]

Looks good! thanks @romac