fix: batch process bug

[parketh]

Summary

This PR fixes a bug introduced in the batch processing refactor in #35.

here, we incorrectly assume that the returned results channel is ordered by height. since block fetching is now async, this channel is actually unordered and needs to first be sorted.

finality-gadget/finalitygadget/finalitygadget.go

Lines 623 to 632 in 0409cd8

	// Extract blocks and find last consecutive finalized block
	var finalizedBlocks []*types.Block
	var lastFinalizedHeight uint64
	for block := range results {
	if block == nil {
	break
	}
	finalizedBlocks = append(finalizedBlocks, block)
	lastFinalizedHeight = block.BlockHeight
	}

the impact of this change was that not all finalized blocks were inserted to the db, even though the latest finalized height advances correctly

besides the fix, we also update FG to:

• allow it to recover from local state after crashes / restarts
• add more debugging logs
• add a new env var in config.toml to set the log level at runtime

Test plan

make test

This bug wasn't caught by previous tests because it doesn't fall under scope of the unit tests (we mock DB inserts to keep the DB implementation generic). It would have been caught by e2e tests, but we deferred this task in favour of testing on the live network.

In the future, we should:

• add e2e test cases to prevent code regression
• add more debugging logs so we can catch bugs more easily in live testing

[SebastianElvis]

can we use a log level enum for this?

[parketh]

makes sense - fixed!