refactor: improve config validation in precise-prefix-cache-scorer

[lisperz]

Summary

This PR improves the precise-prefix-cache-scorer plugin by adding proper configuration validation and extracting magic numbers to named constants.

Changes

1. Extract hardcoded timeout to constant

   • Moved the 10-minute subscription timeout to a named constant defaultSubscriptionTimeout
   • Makes the value more maintainable and self-documenting

2. Add pod discovery configuration validation

   • Validates that podDiscoveryConfig is present when discoverPods is enabled
   • Validates socket port is within valid range (1-65535)
   • Returns clear error messages for invalid configurations

3. Add unit tests

   • Created comprehensive tests for the new validation logic
   • Covers edge cases: missing config, invalid ports (zero, negative, too large)

Motivation

Without validation, invalid configurations could cause runtime panics when the scorer tries to access nil pointers or use invalid port numbers. This change catches configuration errors early during plugin initialization with clear error messages.

Testing

go test ./pkg/plugins/scorer -run TestNew_PodDiscoveryValidation -v

All new validation paths are covered by unit tests.

[github-actions]

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