Signers should not issue rejections if a block has already reached consensus during validation

[jacinta-stacks]

I was seeing the mock GSM signer issuing rejections in an unexpected case (seems to be the case in non GSM signer case as well). Essentially was seeing the singer block reject a block with "Miner's block proposal does not confirm as many blocks as we expect" and it is because in the validate path it wasn't actually checking if the block it was examining had reached consensus in between the validation submission and the validation response. It correctly checks the consensus case in the signature path just not the validation path. This should get rid of these red herring rejections. Still adding a test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.68%. Comparing base (3d27a91) to head (aee2acb).

❗ There is a different number of reports uploaded between BASE (3d27a91) and HEAD (aee2acb). Click for more details.

HEAD has 10 uploads less than BASE

Flag	BASE (3d27a91)	HEAD (aee2acb)
	73	63

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #6826       +/-   ##
============================================
- Coverage    78.33%   60.68%   -17.65%     
============================================
  Files          589      589               
  Lines       357076   357076               
============================================
- Hits        279700   216694    -63006     
- Misses       77376   140382    +63006     

Files with missing lines	Coverage Δ
stacks-signer/src/v0/signer.rs	76.54% <100.00%> (-0.93%)	⬇️

... and 418 files with indirect coverage changes

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