Add TCP stream buffering to SessionInitiationProtocol

[Copilot]

data_received() assumed each TCP chunk was exactly one complete SIP message. TCP is a stream protocol — frames can be split across multiple deliveries or coalesced into one.

Changes

• recv_buffer: bytearray — accumulates raw bytes from the TCP stream across data_received() calls
• PING / PONG constants — module-level typing.Final[bytes] constants (b"\r\n\r\n" and b"\r\n") replace all scattered byte literals in the keepalive path
• extract_frames() — generator that extracts complete frames from the buffer using Content-Length header framing (RFC 3261 §18.3); yields a memoryview into the buffer for each SIP message (zero-copy until Message.parse needs bytes) and the PING/PONG constants for keepalive frames; the view is explicitly released before the buffer is compacted; partial messages remain buffered until all bytes arrive
• dispatch_frame() — routes a single complete frame (memoryview | bytes) to the appropriate handler, converting to bytes only at parse time
• data_received() — appends to recv_buffer and iterates the extract_frames() generator

def data_received(self, data: bytes) -> None:
    self.recv_buffer.extend(data)
    for frame in self.extract_frames():
        self.dispatch_frame(frame)

Tests

39 new tests covering: split headers, split body, coalesced messages, all keepalive edge cases (partial PING, PONG-then-message, etc.), invalid Content-Length, and end-to-end data_received reassembly scenarios.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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  Files                   ?       26           
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  Hits                    ?     1713           
  Misses                  ?      241           
  Partials                ?        0           

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[codingjoe]

@copilot instead of all the comments, try naming constants instead of byte literals for things like ping and pong. We also want to avoid copying too much data here and keep a low memory profile.

[Copilot]

@copilot instead of all the comments, try naming constants instead of byte literals for things like ping and pong. We also want to avoid copying too much data here and keep a low memory profile.

Done in 78daf19. Added PING = b"\r\n\r\n" and PONG = b"\r\n" as typing.Final[bytes] module-level constants. All byte literals in the keepalive path are replaced with these, removing the need for inline comments. extract_frames also yields them directly for keepalive frames (no copy), and dispatch_frame + send_keepalive use them throughout.