fix(agents/relayer): update metrics even if no new event is found

[aroralanuk]

Description

• Follow up to feat(relayer): relayer exposes latest tree index as metric #5074, the cursor_max_sequence(event_type="merkle_tree_insertion") will be used for the highest merkle index on a chain. The logic to update this metric has been moved to when checking for new logs so we can update the metrics even if new events are not found.
• Renamed latest_leaf_index to latest_tree_insertion_index for clarity.

Related #5151

Drive-by changes

None

Related issues

• fixes https://github.com/hyperlane-xyz/issues/issues/1396

Backward compatibility

Yes

Testing

e2e + Manual

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⚠️ No Changeset found

Latest commit: a8d63c2

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.53%. Comparing base (5f9a7c8) to head (a8d63c2).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5178   +/-   ##
=======================================
  Coverage   77.53%   77.53%           
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  Files         103      103           
  Lines        2110     2110           
  Branches      190      190           
=======================================
  Hits         1636     1636           
  Misses        453      453           
  Partials       21       21           

Components	Coverage Δ
core	87.80% <ø> (ø)
hooks	79.39% <ø> (ø)
isms	83.68% <ø> (ø)
token	91.27% <ø> (ø)
middlewares	79.80% <ø> (ø)