Check the size of PROTMESSID_ACKN messages - #302

Introduces src/test/, a QtTest-based unit test target (jamulus-test)
covering CProtocol's on-wire framing contract:

  - golden-frame tests pin the exact bytes production emits today for a
    fixed-length and a variable-length message body, so any accidental
    wire format change fails loudly instead of silently -- the expected
    hex string is built field by field (TAG, message ID, sequence
    counter, data length, data, CRC), each `+=` line commented with what
    that field is, against a fresh CProtocolTester's SentFrames()
  - a frame acceptance/rejection contract test trio (AcceptValidFrame,
    RejectInvalidFrame with bad CRC/length/truncation/junk rows, and
    IgnoreAcknWithEmptyBody -- the regression test for
    jamulussoftware#302, fixed in
    024ebb4: an ACKN message with a valid checksum but no data caused
    an out-of-bounds read; the crafted frame is still well-formed so
    it's accepted at the frame level, but must be silently dropped with
    no signal fired, and the ASan/UBSan matrix job is what gives the
    "no OOB" part of that its teeth) checks how many frames the
    receiving side actually parsed and accepted, building each frame
    imperatively from a real sent frame (LastSentFrame()) plus a small
    set of named mutation helpers
  - one round-trip test through a connected sender/receiver pair
    (CProtocolTester) sends a message on one side and asserts, against
    an event log of everything the other side received, that exactly
    the expected signal fired with the expected arguments

CProtocolTester (src/test/protocoltester.h) is the one public type this
header exposes: a struct-like pair of CProtocol instances (Sender,
Receiver) wired together in both directions -- the same wiring CChannel
uses for two peers, including routing acknowledgements back so the
sender's queue advances -- plus:

  - a sent frame log: every frame Sender hands to MessReadyForSending is
    recorded as both a hex string (SentFrames(), for golden frame
    comparisons) and raw bytes (LastSentFrame(), for tests that mutate a
    real frame); a fresh instance's first send has sequence counter 0,
    which is what makes golden frames byte-for-byte reproducible
  - a receiver-side acceptance count: ReceivedAndAcceptedMessageCount()
    counts frames that passed frame parsing on the receiver side and
    were handed to ParseMessageBody(); a failed parse -- whether from a
    real send or a malformed frame injected via SendRawBytes() -- is a
    silently dropped, countable non-event rather than an assertion
    failure, and is tracked per direction so an ACK flowing back to the
    sender never affects the receiver's own count
  - a received signal log: every non-CLM "receiving" signal CProtocol
    emits from ParseMessageBody (protocol.h's
    ChangeJittBufSize..RecorderStateReceived block, 21 signals) is wired
    to append one formatted "SignalName(arg1, arg2)" line to
    ReceivedLog(), so a test can QCOMPARE the whole log against what it
    expects -- which also proves, for free, that no other wired signal
    fired
  - ToByteArray()/FromByteArray(), the frame mutators
    TruncateBy()/CorruptCRC()/SetDeclaredLength(), and ReplaceIdAndBody()
    (rebuilds a frame with a different ID/body, recomputing length and
    CRC) for crafting ID/body combinations a real Create*Mes() call
    can't produce

Tests hold their own frames/expectations and call these helpers
directly, with no builder chain, lambda-taking capture function, or
shared error-message plumbing in the public surface to look through.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HGdLtGxMrbExBFG3aReNAH