What do these changes do?

This PR fixes a memory consumption issue where IOBasePayload and TextIOPayload would read entire files into memory when streaming large files. The bug was introduced in #10915 and caused the payload classes to read remaining_content_length bytes at once instead of chunking the reads.

The fix ensures that both payload classes never read more than READ_SIZE (64KB) at a time, regardless of the file size or content length. This prevents out-of-memory errors when uploading large files using file-like objects with the aiohttp client.

Are there changes in behavior for the user?

No behavioral changes for users. The fix is transparent and only affects memory usage during file streaming. Files are still uploaded correctly, but now they're read in 64KB chunks instead of potentially reading gigabytes into memory at once.

Is it a substantial burden for the maintainers to support this?

No, this is a minimal fix that restores the original intended behavior. The changes are:

• Adding READ_SIZE as the first parameter to min() in _read_and_available_len() for both IOBasePayload and TextIOPayload
• Ensuring the _read() method is called with appropriate chunk sizes
• Comprehensive test coverage to prevent regression

The fix is straightforward and maintains backward compatibility while fixing a critical memory issue.

Related issue number

Fixes #11138

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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