Add logger package for shared logging across ToolHive projects

[niveshdandyan]

Summary

Adds a shared logger package to toolhive-core for use by ToolHive Runtime, Registry, and other ToolHive ecosystem projects.

Related to stacklok/toolhive#3614

Changes

• Added logger package with structured logging capabilities
• Supports both structured (JSON) and unstructured (human-readable) output
• Integration with logr.Logger for Kubernetes controller compatibility
• Configurable debug mode via DebugProvider interface
• Environment-based configuration via UNSTRUCTURED_LOGS env var
• Added comprehensive test coverage

Features

The logger package provides:

• Multiple log levels: Debug, Info, Warn, Error, Panic, DPanic, Fatal
• Flexible output: Structured JSON or unstructured human-readable format
• Kubernetes integration: NewLogr() for controller-runtime compatibility
• Dependency injection: DebugProvider interface for configurable debug mode
• Testing support: InitializeWithOptions() for test isolation

API

// Initialize with default (non-debug) mode
logger.Initialize()

// Initialize with custom debug provider
logger.InitializeWithDebug(myDebugProvider)

// Initialize with full options for testing
logger.InitializeWithOptions(envReader, debugProvider)

// Logging functions
logger.Debug("message")
logger.Debugf("format %s", arg)
logger.Debugw("message", "key", value)
// ... same pattern for Info, Warn, Error, Panic, DPanic, Fatal

Testing

• go build ./... succeeds
• go test ./... passes

AI Transparency

This PR was created with the assistance of AI (Claude by Anthropic) for code generation and review.

[eleftherias]

Thanks for the PR @niveshdandyan. In the future, please comment on the issue so we can assign it to you before creating pull requests. This helps us coordinate contributions and avoid work duplication. Please check the contribution process here https://github.com/stacklok/toolhive/blob/main/CONTRIBUTING.md#claiming-an-issue

[niveshdandyan]

Thank you for the feedback @eleftherias! I apologize for not following the contribution process properly. I will make sure to comment on issues first to get them assigned before creating PRs in the future. I've noted the contribution guidelines.