feat: add report_calls prometheus metric for Report gRPC method

[RohanKaran]

Fixes #440

Adds a new report_calls Prometheus counter to track calls to the Report gRPC method introduced in #439.

The new metric follows the same pattern as the existing authorized_calls and limited_calls counters:

# HELP report_calls Report calls
# TYPE report_calls counter
report_calls{limitador_namespace="test_namespace"} 5

Changes

• Register report_calls counter with describe_counter! in PrometheusMetrics
• Add incr_report_calls() helper on PrometheusMetrics
• Call incr_report_calls() in KuadrantService::report() after a successful update_counters call
• Add unit tests in prometheus_metrics.rs and kuadrant_service.rs

Summary by CodeRabbit

• Chores

  • Improved system observability by introducing new Prometheus metrics to track reporting activity by namespace, providing enhanced visibility into performance patterns and resource utilisation across different environments.

• Tests

  • Added unit tests to validate the accuracy of new metrics tracking and ensure correct namespace-based measurement.

[coderabbitai]

📝 Walkthrough

Walkthrough

A new Prometheus counter metric report_calls tracks invocations of the Report gRPC method. The PrometheusMetrics struct gains an incr_report_calls method, and KuadrantService::report increments this metric when handling requests. Unit tests verify the metric is correctly recorded per namespace.

Changes

Report Metrics Tracking

Layer / File(s)	Summary
Metric Definition limitador-server/src/prometheus_metrics.rs (line 69)	New Prometheus counter report_calls is registered via describe_counter!.
Metric Increment Logic limitador-server/src/prometheus_metrics.rs (lines 100–104)	incr_report_calls method increments the counter with namespace and context-derived labels, following the pattern of existing metrics.
Integration limitador-server/src/envoy_rls/kuadrant_service.rs (lines 167–173)	KuadrantService::report calls self.metrics.incr_report_calls to record each report invocation.
Tests limitador-server/src/prometheus_metrics.rs (lines 410–442), limitador-server/src/envoy_rls/kuadrant_service.rs (lines 622–697)	Unit tests verify report_calls is incremented and emitted correctly per namespace.

Estimated Code Review Effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 The Report now whispers its tale,
Each call counted, metrics prevail,
Prometheus hears every chime—
A counter that tracks passing time! 📊✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 63.64% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding a new Prometheus metric for the Report gRPC method.
Linked Issues check	✅ Passed	The PR fully addresses issue #440 by implementing the report_calls Prometheus counter metric with namespace labels as requested.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing the report_calls metric; no out-of-scope modifications detected.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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