feat(services): add OpenTelemetry tracing to Storage, Function, Database, and Cache services

[poyrazK]

Summary

Instrument StorageService, FunctionService, DatabaseService, and CacheService with OpenTelemetry spans for improved observability. Closes #339.

This supersedes PR #369 (now closed — it accidentally included unrelated resource-limit changes).

Changes

• StorageService (storage-service): Upload, Download, CreateBucket, DeleteBucket
• FunctionService (function-service): CreateFunction, InvokeFunction, GetFunctionLogs
• DatabaseService (database-service): CreateDatabase, RestoreDatabase, doRotateCredentials
• CacheService (cache-service): CreateCache, GetCacheStats

Implementation

Each method follows the established OTel pattern:

tracer := otel.Tracer(tracerName)
_, span := tracer.Start(ctx, "Service.Method",
    trace.WithAttributes(
        attribute.String("field", value),
    ))
defer span.End()
// ... existing logic ...
if err != nil {
    span.RecordError(err)
    return nil, err
}

Uses _ for the span-wrapped context to avoid propagating trace context into repo/mock calls (which would break mock equality assertions in unit tests).

Test Plan

• go build ./internal/core/services/...
• go test ./internal/core/services/... -count=1 (all pass)

Verification

With TRACING_ENABLED=true and Jaeger running locally, traces will appear at http://localhost:16686.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: deed6d11-792d-435a-a768-02e8e5c2ebe1

📥 Commits

Reviewing files that changed from the base of the PR and between b4819c0 and 2e6a0f4.

📒 Files selected for processing (4)

• internal/core/services/cache.go
• internal/core/services/database.go
• internal/core/services/function.go
• internal/core/services/storage.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/opentelemetry-tracing-v2

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