chore: add subscription activation and per-program metrics

[thlorenz]

Summary

Add metrics for tracking gRPC subscription activations and per-program account updates to
better monitor subscription behavior and account update patterns.

Details

Added two new metrics to track subscription and account update activity:

Subscription Activation Tracking

• account_subscription_activations_count: Tracks when new account subscriptions are activated, labeled by client_id

Per-Program Account Updates

• per_program_account_updates_count: Tracks all account updates received grouped by program ID, labeled by both client_id and program
• Updated program_subscription_account_updates_count description to clarify it only counts updates matching existing subscriptions

Summary by CodeRabbit

Release Notes

• New Features
  • Subscription Activation Tracking: Metrics now capture account subscription activation events for improved visibility into subscription lifecycle.
  • Per-Program Account Updates: New metrics provide detailed insights into account updates by program, enabling better analysis of activity patterns and system behavior.

[github-actions]

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[coderabbitai]

📝 Walkthrough

Walkthrough

The changes add new observability metrics to track account subscription activations and per-program account updates across the codebase. Two new metrics are introduced in the metrics module: ACCOUNT_SUBSCRIPTION_ACTIVATIONS_COUNT and PER_PROGRAM_ACCOUNT_UPDATES_COUNT, along with corresponding public API functions. These metrics are integrated into the chain laser actor and chain pubsub actor to increment counters when subscription activations occur and when program-sourced account updates are processed.

Suggested reviewers

• GabrielePicco
• bmuddha
• lucacillario

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch thlorenz/grpc-metrics

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@magicblock-metrics/src/metrics/mod.rs`:
- Around line 301-309: The metric PER_PROGRAM_ACCOUNT_UPDATES_COUNT currently
uses a free-form "program" label which can explode Prometheus cardinality;
change this by replacing the free-form label with a bounded alternative: either
remove the "program" label and aggregate by client only, introduce a
validated/allowlisted program label (accept only known program IDs) or map
program IDs to a fixed set of buckets/hashes (e.g., canonical names or safe
short buckets) before incrementing the IntCounterVec; implement the guard in the
code path that calls
PER_PROGRAM_ACCOUNT_UPDATES_COUNT.inc_with_label_values(...) so only
allowed/mapped values are used, or add a sanitization function (e.g.,
map_program_label) referenced where the metric is updated to enforce the bounded
set.

[bmuddha]

LGTM