Add block support to rescue_from for custom error handling

[obie]

Summary

This PR adds block support to the rescue_from method, allowing services to customize error handling with full control over the response.

Motivation

Currently, rescue_from only supports a static error type via the use: parameter. This PR enables dynamic error handling by accepting a block that can:

• Return custom failure messages
• Return success despite catching an exception
• Dynamically choose error types

Implementation

The implementation uses a BlockContext class that provides success() and failure() methods matching the service interface. The block is executed via instance_exec, giving a natural API:

rescue_from SomeError do |e|
  failure("Custom error: #{e.message}")
end

Key Features

• Clean API: No extra parameters needed - just call success/failure directly
• Full backward compatibility: Existing rescue_from declarations continue to work
• Multiple handlers: Different blocks can handle different error types
• Recovery from errors: Can return success despite catching an exception

Testing

Comprehensive test coverage includes:

• Custom failure messages
• Returning success despite exceptions
• Dynamic error type selection
• Multiple rescue_from blocks
• Backward compatibility verification

All existing tests pass without modification.

Example Usage

class MyService < Servus::Base
  # Custom error message
  rescue_from ActiveRecord::RecordInvalid do |e|
    failure("Failed to save: #{e.message}")
  end
  
  # Recover from error
  rescue_from RetryableError do |e|
    Rails.logger.warn("Recovered from: #{e.message}")
    success({ recovered: true, fallback_used: true })
  end
  
  # Dynamic error type
  rescue_from ValidationError do |e|
    failure(e.message, type: Servus::Support::Errors::UnprocessableEntityError)
  end
  
  # Old syntax still works
  rescue_from OtherError, use: Servus::Support::Errors::NotFoundError
end