feat: cursor metrics

[Mantas-M]

Description

Adds metrics to ForwardBackward cursor in order to be able to monitor sync progress more effectively.

Introduced metrics

• cursor_current_block: Which block is the forward and backward cursor indexing currently for each event
  
  Example above shows all event average

• cursor_current_sequence: Which sequence is the cursor currently on for a specific event
  
  As in the graph for Base above, we can see that the Forward cursor only begins showing data if there are new events to index since agent launch

• cursor_max_sequence: The max sequence the cursor can reach

Related issues

• Fixes Expose metrics for sequence indexing cursor progress #4715

Backward compatibility

Yes

Testing

Manual

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[Mantas-M]

Read the issue again and I thought to refactor the metrics to be cursor generic due to this requirement set by @daniel-savu
for all event types (regardless if sequenced or not): the block number the cursor(s) are currently at

Initially seems like it would be not necessary due to the contract_sync_block_height metric doing mostly the same thing:

But this makes it cleaner in my opinion and when/if the internal Grafana dashboards would be migrated to the new metric, contract_sync_block_height could be removed entirely.

Now with the CursorMetrics being passed in to both the RateLimitedContractSyncCursor and the ForwardBackwardSequenceAwareSyncCursor we get a more verbose group of metrics from both sequence aware and non sequence aware event indexing cursor block heights:

Additionally, since the implementation of name on the Indexable trait, we could technically remove the label strings passed into the sync function making it a bit nicer and keeping all the hardcoded strings on the Indexable trait implementation.

[ameten]

I wonder if values forward_rate_limited and backward_rate_limited are valid for this metric?

[Mantas-M]

forward_rate_limited is indeed valid as it's the only mode for the RateLimitedCursor, as seen here

backward_rate_limited removed in both occurrences.