Add xunit.runner.explicit.json to disable test parallelism

Added a new xunit.runner.explicit.json config file that disables parallelization at both the assembly and test collection levels, sets maxParallelThreads to 1, and uses the "conservative" parallel algorithm. Also includes a $schema reference for validation.

Author: kzdev-net

Source/Tst/xunit.runner.explicit.json

@@ -0,0 +1,7 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeAssembly": false,
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1,
+  "parallelAlgorithm": "conservative"
+}