Fix the AckSendDelay test

[guhetier]

Description

The AckSendDelay test was flaky and of doubtful utility:

• it asserts there was only a single ACK received after a client send a buffer, which isn't fully true: other frames can be sent for reasons outside of the test control (for instance, NEW_CONNECTION_ID).

• the ack delay feature tested is more about whether an ACK is eventually sent if no other ack-eliciting frame is received, and less about whether an ack piggy-pack on the next frame sent by the server (which is an MsQuic implementation detail)

The test is re-written to validate an ACK is received within a reasonable amount of time after a send.

Testing

N/A

Documentation

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.33%. Comparing base (bb17196) to head (e2710af).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5125      +/-   ##
==========================================
- Coverage   85.93%   85.33%   -0.61%     
==========================================
  Files          59       59              
  Lines       18048    18048              
==========================================
- Hits        15510    15401     -109     
- Misses       2538     2647     +109     

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