Persist StateProof builders on disk

[Aharonee]

To support indefinite StateProofs recovery period (currently only 1000 intervals are supported), we must store the date required to build a StateProof transaction on disk.
This feature is a partial implementation, migrating the existing database and adding logic for persisting and restoring StateProof builders, as well as updating the unit tests accordingly.

Persist StateProof Builders

• Add flag (used by Relay nodes) to enable this feature
• Migrate the StateProof database
• Insert every new builder into the database
• Delete entry when the relevant StateProof transaction was confirmed
• Load from DB (if flag enabled) on startup

Keep less builders in memory and send less signatures

This will be implemented in a separate PR

• Replace the builders map with 2 (more?) builders: NextStateProofRoundBuilder and LatestRoundBuilder.

Testing

• Enable persistBuilder flag for every test to make sure nothing breaks
• Write new unit tests to verify the database state
• Test: the number of builders in DB is consistent with the number of pending StateProofs
• Test: if stateproof is not stalled, there should only be one builder stored in DB
• Fix tests in worker_test.go to timeout when waiting on txmsg channel instead of blocking indefinitely
• Update unit tests to make sure number of builders in memory is consistent with that in DB (will change in the next PR when limiting memory footprint)
• Write e2e tests?

[codecov]

Codecov Report

Merging #4553 (dda383d) into feature/stateproofs-recoverability (7de989a) will increase coverage by 0.09%.
The diff coverage is 78.88%.

@@                          Coverage Diff                           @@
##           feature/stateproofs-recoverability    #4553      +/-   ##
======================================================================
+ Coverage                               55.23%   55.33%   +0.09%     
======================================================================
  Files                                     398      398              
  Lines                                   50276    50389     +113     
======================================================================
+ Hits                                    27772    27881     +109     
+ Misses                                  20188    20185       -3     
- Partials                                 2316     2323       +7     

Impacted Files	Coverage Δ
node/node.go	4.43% <ø> (ø)
stateproof/db.go	79.77% <74.07%> (-4.44%)	⬇️
stateproof/builder.go	80.14% <78.26%> (+3.22%)	⬆️
stateproof/signer.go	52.38% <80.00%> (+1.74%)	⬆️
crypto/stateproof/builder.go	88.88% <89.28%> (-0.64%)	⬇️
stateproof/worker.go	89.28% <100.00%> (-0.72%)	⬇️
network/wsNetwork.go	64.63% <0.00%> (-0.20%)	⬇️
ledger/acctupdates.go	69.89% <0.00%> (+0.59%)	⬆️
catchup/service.go	68.88% <0.00%> (+0.74%)	⬆️
... and 3 more

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[id-ms]

Overall looks good.
Have some suggestions to have a clearer code.