test: revert Core.Net serialization; widen the virtual-clock harness patience instead

Serializing AcDream.Core.Net.Tests to fix a Linux starvation REGRESSED Windows,
which had been green: Core.Net went from 1000 passed in 7 s (run 154) to
999/1000 in 17 s (run 155), taking down LossSoak_TwoPercentBidirectional_
ZeroMessageLoss_LedgersConverge, a test that had never failed. That trade trans-
ferred the flake between platforms rather than fixing anything, so it is
reverted: no xunit.runner.json, no csproj change.

The actual fragility is narrower than it looked — exactly ONE test uses
real-time waits (PausedSelector_SeededDroppedServerReady_RecoversOnIdleSweep),
and its harness drives a VIRTUAL clock while asserting on 2 s wall-clock
windows. Those windows are patience for background work, not part of the
assertion, and 2 s only ever encoded 'the machine is idle'. They now share a
60 s HarnessPatience constant.

Nothing about what the test verifies changes: recovery must still occur, a
genuine failure to NAK still fails, and a real hang is still bounded. Campaign N
transport code is untouched.

Local: 1000/1000 in 6 s under the gate filter.

tests/AcDream.Core.Net.Tests/AcDream.Core.Net.Tests.csproj

@@ -22,15 +22,4 @@
     <ProjectReference Include="..\..\src\AcDream.Core.Net\AcDream.Core.Net.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <!-- Several transport tests drive a virtual clock but assert on REAL-time
-         waits (2 s SpinUntil windows). Under default parallelism on a small CI
-         container PausedSelector_SeededDroppedServerReady_RecoversOnIdleSweep
-         took 37-42 s and missed its window, while passing 5/5 in ~350 ms in
-         isolation on the same machine. Serialize the assembly rather than
-         loosen a Campaign N transport assertion. Same settings
-         AcDream.Core.Tests and AcDream.Launcher.Tests already use. -->
-    <None Update="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
-  </ItemGroup>
-
 </Project>