feat(tracing): add type-state builder pattern for configuration

[kariy]

Summary

Implements a fluent builder pattern with compile-time guarantees for configuring tracing/logging features in the katana-tracing crate.

Motivation

The current tracing initialization uses a single init() function that takes all configuration at once. This PR introduces a type-state builder pattern that:

• Enforces correct configuration at compile-time
• Prevents mutually exclusive configurations (e.g., OTLP and Google Cloud telemetry)
• Provides a more intuitive and flexible API
• Maintains full backward compatibility

Changes

• Added TracingBuilder with type-state pattern for compile-time safety
• Implemented separate builder states for configuration flow
• Added support for custom service names in telemetry backends
• Created comprehensive examples demonstrating builder usage
• Updated existing init() function to use builder internally (backward compatible)

API Usage

// Basic configuration
TracingBuilder::new()
    .with_log_format(LogFormat::Json)
    .with_default_filter()?
    .configure()
    .build()
    .await?;

// With OTLP telemetry
TracingBuilder::new()
    .with_service_name("my-katana-node")
    .configure()
    .with_telemetry()
    .otlp()
    .with_endpoint("http://localhost:4317")
    .build()
    .await?;

// With Google Cloud telemetry  
TracingBuilder::new()
    .configure()
    .with_telemetry()
    .gcloud()
    .with_project_id("my-project")
    .build()
    .await?;

Type-State Pattern Benefits

• Compile-time validation: Invalid configurations are caught at compile time
• Mutually exclusive telemetry: Once you choose OTLP or Google Cloud, you cannot configure the other
• Single direction flow: Configuration progresses forward only, preventing inconsistent states
• Required vs optional: Clear distinction between required and optional configurations

Testing

• Added unit tests for builder pattern
• Created comprehensive examples in examples/builder_usage.rs
• All existing tests continue to pass

Backward Compatibility

The existing init() function is preserved and now uses the builder internally, ensuring no breaking changes for existing code.

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com