fix LimitedStream.read method to work with raw IO streams

[thrau]

This PR adds a test and fix for LimitedStream to work with raw IO streams. Raw IO streams can return fewer bytes than passed to size in a read call, and previously LimitedStream.read was not equipped to handle these cases.
I had to

• add a method to deal with cases where LimitedStream.read(-1) is called, that would exhaust the remainder of the stream and actually return the result. It uses a common "read into buffer" pattern.
• change the condition on what the read method considers as a client disconnect. The added tests should clarify further what is considered a disconnect and what isn't.

• fixes LimitedStream not respecting read contract of RawIOBase. #2558

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[thrau]

could i get your sentiment whether this is in principle an acceptable solution @davidism? happy to then complete the other PR tasks and investigate the failing checks.

[davidism]

Refactored this to fix exhaust as well and use the same logic for both. Previously, exhaust was assuming that read would return the size that was requested. Also added a changelog and comments to the code and test.

[thrau]

thanks a lot for pushing it over the line @davidism 🙏