feat: api and indexer instrumented with metrics

[dhyaniarun1993]

Closes #205

[codecov-commenter]

Codecov Report

❌ Patch coverage is 11.39896% with 684 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@523cfdb). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/indexer/store/instrumented.go	0.00%	143 Missing ⚠️
pkg/ethrpc/store/instrumented.go	0.00%	110 Missing ⚠️
pkg/userstore/instrumented.go	0.00%	86 Missing ⚠️
pkg/indexer/client/instrumented.go	0.00%	53 Missing ⚠️
pkg/app/api/server.go	0.00%	44 Missing ⚠️
pkg/app/indexer/server.go	0.00%	28 Missing ⚠️
pkg/app/http/metrics.go	0.00%	25 Missing ⚠️
pkg/ethrpc/store/metrics.go	0.00%	22 Missing ⚠️
pkg/indexer/store/metrics.go	0.00%	22 Missing ⚠️
pkg/transfer/cache_instrumented.go	0.00%	21 Missing ⚠️
... and 11 more

❌ Your patch status has failed because the patch coverage (11.39%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #221   +/-   ##
=======================================
  Coverage        ?   30.65%           
=======================================
  Files           ?      140           
  Lines           ?     9246           
  Branches        ?        0           
=======================================
  Hits            ?     2834           
  Misses          ?     6175           
  Partials        ?      237           

Flag	Coverage Δ
unittests	30.65% <11.39%> (?)

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

Files with missing lines	Coverage Δ
pkg/config/config.go	71.69% <ø> (ø)
pkg/ethrpc/miner/metrics.go	100.00% <100.00%> (ø)
pkg/ethrpc/miner/miner.go	97.50% <100.00%> (ø)
pkg/indexer/engine/metrics.go	100.00% <100.00%> (ø)
pkg/indexer/engine/processor.go	83.33% <100.00%> (ø)
pkg/relayer/engine/metrics.go	94.95% <100.00%> (ø)
internal/metrics/metrics.go	0.00% <0.00%> (ø)
pkg/cantonsdk/client/options.go	0.00% <0.00%> (ø)
pkg/relayer/store/metrics.go	0.00% <0.00%> (ø)
pkg/app/relayer/server.go	0.00% <0.00%> (ø)
... and 17 more

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[gemini-code-assist]

Code Review

This pull request implements comprehensive Prometheus metrics instrumentation across the API server, indexer, relayer, and Canton SDK, including dedicated monitoring endpoints and updated deployment configurations. It also introduces a robust suite of end-to-end tests covering user registration, JSON-RPC facades, and bridge deposit/withdrawal flows. Feedback highlights the need to remove an outdated compile-time guard in the API middleware, address a risky type assertion in the instrumented indexer store to prevent potential panics, and refactor the indexer's monitoring server initialization to ensure architectural consistency across the codebase.