feat(e2b): add prometheus metrics for core api operations

[PRAteek-singHWY]

[Observability] Add Prometheus Metrics for E2B API Operations

Summary

This PR enhances the observability of the sandbox-manager by instrumenting core E2B API operations with Prometheus metrics. It provides visibility into API latency and success/error rates for sandbox lifecycle events.

Problem

Currently, the sandbox-manager only tracks snapshot operations. Core lifecycle events such as creating, deleting, and updating timeouts for sandboxes lack duration and request count tracking at the API layer. This makes it difficult to monitor the performance and reliability of the E2B-compatible API gateway.

Solution

Implemented a unified metrics pattern in pkg/servers/e2b/metrics.go and instrumented the corresponding handlers:

1. Unified Metrics:
   • sandbox_api_operation_duration_seconds (Histogram): Tracks latency by operation (create, delete, describe, timeout, snapshot) and result (success, error).
   • sandbox_api_operation_total (Counter): Tracks total requests by operation and result.
2. Instrumentation:
   • Instrumented CreateSandbox in create.go.
   • Instrumented DeleteSandbox and DescribeSandbox in services.go.
   • Instrumented SetSandboxTimeout in timeout.go.
   • Refactored CreateSnapshot in snapshot.go to use the new unified pattern, removing legacy snapshot-specific metrics.
3. Code Quality:
   • Used named return parameters and defer blocks in handlers for robust metric collection.
   • Ensured consistent bucket sizes (20ms to ~41s) for all API histograms.

Verification

• Unit Tests: Ran go test -v ./pkg/servers/e2b/... and confirmed all 26.2s of tests pass.
• Metric Registration: Verified that new metrics are correctly registered in the global Prometheus registry.
• Go Version: Verified with Go 1.25.0.

Checklist

• Define new Prometheus metrics in pkg/servers/e2b/metrics.go.
• Implement instrumentation in API handlers.
• Migrate existing snapshot metrics to the new pattern.
• Verify with unit tests.

fixes #332

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.81%. Comparing base (edaad73) to head (e790f5b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #333      +/-   ##
==========================================
+ Coverage   74.65%   74.81%   +0.15%     
==========================================
  Files         141      141              
  Lines        9836     9870      +34     
==========================================
+ Hits         7343     7384      +41     
+ Misses       2183     2179       -4     
+ Partials      310      307       -3     

Flag	Coverage Δ
unittests	74.81% <100.00%> (+0.15%)	⬆️

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[PRAteek-singHWY]

Hi @furykerry, @AiRanthem, and @zmberg

In this PR, I have instrumented the core E2B API operations (Create, Delete, Describe, Timeout) with Prometheus metrics to track latency and success rates. I also unified the existing snapshot metrics into this new schema and added unit tests to ensure 100% coverage of the instrumentation.
Always ready to iterate based on your guidance.

Looking forward to your feedback.

Thank You.