Add new attributes on metrics register

[joaopaulovieira]

Main Changes

1. Context and Request ID

• Refactored the use of context key for request ID:
  • The key type is now exported (ContextRequestIDKey) and uses a safer name to avoid collisions.
  • The function to retrieve the request ID from context (RequestID) is now public and used throughout the project.
  • Usage of the function was updated in transport.go and in tests.

2. Tests

• Context, request, and suite tests were moved to the httpclient_test package to follow the black box pattern.
• Added unit test for the SetHostURL method in Request.
• Added integration test for metrics using mocks, covering success scenarios.

3. Request

• Added public SetHostURL method to the Request struct.
• Improved test coverage for Request methods.

4. Metrics

• Refactored the registerMetrics function for better control of attributes and metric counters.
• Host and path attributes are now correctly added to metrics.

5. Transport

• Refactored to use the public RequestID function when setting the request ID header.

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Other Adjustments

• Organized imports and removed unused ones.
• Improved comments and documentation for greater clarity.