[MISC]: add vtc_bucket_size_active metric gauge for vtc-basic

[Venkat2811]

Pull Request Description

This change adds:

• vtc_bucket_size_active custom metric gauge to see if any config change is needed in vtc-basic
• centralized metrics utility for custom metrics like the above in this project

Related Issues

#1011 (comment)

Submission Checklist

• PR title includes appropriate prefix(es)
• Changes are clearly explained in the PR description
• New and existing tests pass successfully
• Code adheres to project style and best practices
• Documentation updated to reflect changes (if applicable)
• Thorough testing completed, no regressions introduced

[Jeffwan]

I will take a look at it tomorrow

[Copilot]

Pull Request Overview

This PR introduces a new custom metric gauge, vtc_bucket_size_active, along with centralized metrics utilities to support its use in the vtc-basic algorithm and its tests. Key changes include:

• Adding gauge metric update in the BasicVTCRouter.Route method.
• Extending test coverage with TestVTCBucketSizePatterns and related helper functions.
• Integrating the new metric into the metrics package and updating module dependencies.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/plugins/gateway/algorithms/vtc/vtc_basic_test.go	Added tests for vtc_bucket_size_active metric behavior and patterns
pkg/plugins/gateway/algorithms/vtc/vtc_basic.go	Updated routing logic to record the new metric using adaptiveBucketSize
pkg/metrics/metrics.go	Introduced the constant and configuration for vtc_bucket_size_active
pkg/metrics/custom_metrics_test.go	Added tests for custom metric registration and update behavior
pkg/metrics/custom_metrics.go	Updated helper functions for gauge and counter metric handling
go.mod	Added dependency for godebug

Comments suppressed due to low confidence (2)

pkg/plugins/gateway/algorithms/vtc/vtc_basic_test.go:617

• Consider adding assertions to verify that the detected pattern matches expected outcomes instead of solely logging results for improved test validation.

if pattern.detectFunc(sizes) {

pkg/metrics/custom_metrics.go:94

• The GetGaugeValueForTest function always returns 0; consider implementing it to actually return the current gauge value to improve the reliability of tests referencing it.

return 0

[Jeffwan]

Overall looks good to me!