Fix max frame size

## Problem

Per the message format specification, the frame size is an unsigned 32-bit integer. No other limits are set on this value. As such, the max frame size is `2^32 - 1`, not `2^31 - 1` as currently defined. It looks like this snuck in as an implementation detail from the Java client, where the frame size is limited by `MAX_INT`.

## Solution

Fix the defined value to be `2^32 - 1` and add tests that verify that frames of size `2^31 - 1 < frame_size <= 2^32 - 1` work correctly.

Start by locating the defined maximum frame size and the tests covering frame encoding, decoding, or validation. Verify the current boundary behavior, then update the value and add coverage for sizes above 2^31 - 1 through 2^32 - 1; done means those frames work correctly and the existing tests pass.

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