Add tests for reading a control stream

[tatsuhiro-t]

No description provided.

[Copilot]

Pull Request Overview

This PR adds tests for reading a control stream by modifying the behavior in nghttp3_conn_read_control to return the number of bytes consumed immediately when the input buffer is exhausted.

• Replaces a break with an early return when "p == end" in the frame length state.
• Introduces a similar early return in the priority update state.

Comments suppressed due to low confidence (2)

lib/nghttp3_conn.c:664

• Switching from 'break' to an early 'return' changes the control flow in the state machine. Ensure that all functions calling nghttp3_conn_read_control correctly handle this early return behavior and that no additional frame processing is expected after reaching the end of input.

return (nghttp3_ssize)nconsumed;

lib/nghttp3_conn.c:973

• The early return in the priority update state mirrors the change above. Verify that this change is consistent with the state machine’s overall flow and that all caller logic is updated accordingly.

return (nghttp3_ssize)nconsumed;