Implement InvalidRequestError with field-level validation details

[samueloyibodevv]

Overview

This PR implements InvalidRequestError in the Shade Python SDK so developers get clear, field-level feedback when the API rejects malformed or invalid request parameters. It parses the API error response format, exposes the offending field and all field errors, and raises the exception on HTTP 400/422 responses.

Related Issue

Closes #17

Changes

⚠️ Invalid Request Error Handling

• [MODIFY] src/shade/errors.py
• Expanded InvalidRequestError(ShadeError) with param: Optional[str] and field_errors: dict.
• Added parsing for API error responses such as {"error": {"code": "invalid_param", "param": "amount", "message": "..."}}.
• Added InvalidRequestError.from_response() to construct the exception from raw 400/422 response bodies.
• Added raise_for_invalid_request() to raise InvalidRequestError on HTTP 400 and 422 responses.
• Updated __str__() so the offending parameter name is included in the error message when available.

🧪 Tests

• [MODIFY] tests/test_errors.py
• Added tests for parsing param from API error responses.
• Added tests for parsing field_errors from API error responses.
• Added tests verifying str(error) includes the param name.
• Added tests verifying HTTP 400 and 422 responses raise InvalidRequestError.
• Added tests verifying explicit constructor arguments override parsed body values.
• Added tests verifying non-400/422 status codes do not raise.

Verification Results

pytest tests/test_errors.py tests/test_gateway.py -v ✅ passed (13/13)

Acceptance Criteria	Status
A 400 response raises InvalidRequestError	✅
error.param names the offending field when the API provides one	✅
error.field_errors contains all field-level errors from the API response	✅
str(error) includes the param name in the message	✅

[codebestia]

Hello @samueloyibodevv
Please resolve the conflicts.