feat: add request/response body logging at DEBUG level

[crawfordxx]

Summary

Adds optional logging of HTTP request and response bodies at DEBUG level to aid debugging, addressing #1522.

• Logs request body before sending and response body after receiving
• Gated behind log.isEnabledFor(logging.DEBUG) to avoid performance impact when not enabled
• Skips response body logging for streaming responses to prevent reading the stream prematurely
• Applied to both sync (SyncAPIClient) and async (AsyncAPIClient) code paths

Usage

import logging
logging.basicConfig()
logging.getLogger("openai._base_client").setLevel(logging.DEBUG)

client = openai.OpenAI()
client.chat.completions.create(model="gpt-4", messages=[{"role": "user", "content": "hi"}])
# DEBUG logs will now include request/response bodies

Test plan

• Verify request body appears in DEBUG logs when logging level is set
• Verify response body appears in DEBUG logs for non-streaming requests
• Verify no body logging when log level is INFO or higher
• Verify streaming responses do not log response body
• Verify no performance regression when DEBUG logging is disabled

Closes #1522

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid reading request.content before send

Accessing request.content here can raise httpx.RequestNotRead for multipart or streaming request bodies (for example calls that use files=), because those requests are represented as streams until they are sent/read. Since this happens before the try block around self._client.send(...), enabling DEBUG logging can cause upload endpoints to fail immediately instead of sending the request; the async path has the same pattern.

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