Net: Replace timing-dependent tests with condition-based waiting

[matejk]

Summary

Follow-up to #5137 which introduced waitForCondition() for Foundation tests.

The Net testsuite has similar patterns that could benefit from waitForCondition to eliminate flaky timing-dependent tests.

High Priority (Unbounded Loops)

File	Line	Pattern
PollSetTest.cpp	451	while (!poller.isRunning()) Thread::sleep(100);
UDPServerTest.cpp	122-134	do { Thread::sleep(10); } while (count < i);

Medium Priority (Fixed Sleeps + Assertions)

File	Count	Notes
DatagramSocketTest.cpp	1	Sleep before assertTrue(ss.available() == 5)
WebSocketTest.cpp	4	Sleeps waiting for server start
SyslogTest.cpp	6	Sleeps waiting for syslog processing
TCPServerTest.cpp	10	Sleeps in server tests

Scope

Total: ~49 Thread::sleep calls across 13 files, of which 2 are critical unbounded loops and ~8-10 are good candidates for condition-based waiting.

Pattern to Apply

// Before (unbounded, can hang forever):
while (condition) Thread::sleep(50);

// After (bounded, fails cleanly if condition never met):
assertTrue(waitForCondition([&]{ return condition; }, 5000));

References

• PR fix(Foundation): Replace timing-dependent tests with condition-based waiting #5137 - Foundation condition-based waiting implementation