Update documentation: max_queue exists in threading implementation

[Copilot]

Summary

Fixes the documentation in "Memory and Buffers" topic page which incorrectly stated that max_queue doesn't exist in the threading implementation.

Issue

The documentation stated:

In the :mod:threading implementation, there is no queue of incoming messages. The max_queue argument doesn't exist. The connection keeps at most one message in memory at a time.

However, the threading (sync) implementation does have the max_queue argument and it works the same way as in the new asyncio implementation.

Changes

Updated docs/topics/memory.rst to correctly document that:

• The max_queue argument exists in the threading implementation
• It has the same semantics as the new asyncio implementation
• It is the high-water mark of a queue of incoming frames
• It defaults to 16 frames (same as asyncio)
• It provides backpressure control when the queue grows above the high-water mark

Context

As noted by @aaugustin in the issue, max_queue wasn't in the initial version of the threading implementation but was added later as a performance optimization. The documentation was never updated to reflect this change.

Closes #1544

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Original prompt

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This section details on the original issue you should resolve

<issue_title>"Memory and Buffers" docs and max_queue in threading implementation</issue_title> <issue_description>I believe the topic page "Memory and Buffers" in the documentation might need to be updated - in the end it says:

In the threading implementation, there is no queue of incoming messages. The max_queue argument doesn’t exist. The connection keeps at most one message in memory at a time.

But looks like max_queue exists in the threading implementation - I guess works the same as in the asyncio one?</issue_description>

Comments on the Issue (you are @copilot in this section)

@aaugustin Good catch, thank you. I think it wasn't there in the initial version, then got added later as a performance optimization. Yes it has the same semantics as in the asyncio implementation.

Fixes python-websockets/websockets#1664

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