Implement unified response parser

[codebestia]

Description

All resource methods should go through a single _parse_response(response) function that handles JSON decoding, success detection, and mapping HTTP error codes to the correct typed exceptions. This prevents per-resource error handling drift.

Proposed Steps

• Create _parse_response(response: httpx.Response) -> dict in http_client.py.
• On 2xx: decode JSON and return the dict.
• On 401: raise AuthenticationError.
• On 400 / 422: raise InvalidRequestError with field-level errors if present.
• On 404: raise NotFoundError.
• On 429: raise RateLimitError.
• On 5xx: raise NetworkError (subject to retry).
• On JSON decode failure: raise ShadeError("Invalid response from API").

Acceptance Criteria

• Every 4xx/5xx response is mapped to the correct exception type.
• The raw response body and HTTP status are accessible on every exception.
• A non-JSON response body raises ShadeError rather than crashing with a raw JSONDecodeError.
• 2xx responses that contain an error key in the body are still treated as errors.

[ciynthia]

Hello, this issue aligns well with my skill set and I’m confident I can resolve it properly. Please assign it to me.