feat(driver): Allow the driver to raise errors in some occasions

[romac]

Namely:

• When Env::get_value fails to return a value to propose
• When the supposed proposer cannot be found in the validator set
• When a vote's validator cannot be found in the validator set
• When a vote's signature is invalid

[codecov]

Codecov Report

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

Comparison is base (b2d63ed) 86.45% compared to head (b28e5f0) 86.67%.

Files	Patch %	Lines
Code/driver/src/error.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #62      +/-   ##
==========================================
+ Coverage   86.45%   86.67%   +0.22%     
==========================================
  Files          25       26       +1     
  Lines        1166     1185      +19     
==========================================
+ Hits         1008     1027      +19     
  Misses        158      158              

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