Alex/5857 full fix

[AlexHentschel]

This implements step 1 of https://github.com/dapperlabs/flow-go/issues/5857:

simple fix for the business logic

• update consensus.Builder to always include a gap
  • add test to verify that updated business always leaves a gap
  • update existing tests that broke due to change in business logic
• update sealValidator to enforce the gap
  • add test to verify that verification logic rejects seals without a gap
  • update existing tests that broke due to change in business logic

Context

This PR is an extension of #1307. In this PR, we also update the seal-validation logic to reject seals that do not have a gap.

[codecov-commenter]

Codecov Report

Merging #1325 (5195cdc) into master (864fc75) will increase coverage by 0.00%.
The diff coverage is 52.63%.

@@           Coverage Diff           @@
##           master    #1325   +/-   ##
=======================================
  Coverage   56.23%   56.24%           
=======================================
  Files         500      500           
  Lines       31072    31079    +7     
=======================================
+ Hits        17474    17479    +5     
- Misses      11232    11234    +2     
  Partials     2366     2366           

Flag	Coverage Δ
unittests	56.24% <52.63%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
module/chunks/chunk_assigner.go	58.97% <0.00%> (ø)
module/validation/seal_validator.go	76.10% <50.00%> (-0.75%)	⬇️
state/protocol/badger/snapshot.go	57.32% <66.66%> (ø)
module/builder/consensus/builder.go	70.03% <100.00%> (+0.23%)	⬆️
...ngine/common/synchronization/finalized_snapshot.go	68.75% <0.00%> (-4.17%)	⬇️
admin/command_runner.go	78.51% <0.00%> (-1.49%)	⬇️
engine/collection/synchronization/engine.go	63.97% <0.00%> (+1.07%)	⬆️
...sus/approvals/assignment_collector_statemachine.go	53.84% <0.00%> (+1.92%)	⬆️

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[huitseeker]

One thing that's confusing to me is that this indicates "final", mentions it only implements step 1 of https://github.com/dapperlabs/flow-go/issues/5857, yet:

• seems to tick all boxes for step 2 of 5857,
• contains a "TEMPORARY" all-caps comment.

I feel there's a way to make this PR more kind to a future eng exploring the status of the remediation we're putting in, here.

Otherwise, the code looks good!