Use the test Makefile for all examples

* Rename and move sbysrc/demo[123].sby to docs/examples/demos
    * Make them use multiple tasks for multiple engines
* Scan docs/examples for sby files for make test
* `make ci` is now `NOSKIP` by default
* Skip scripts using `verific` w/o yosys verific support
    * This does not fail even with NOSKIP set

tests/make/test_rules.py

@@ -56,6 +56,9 @@ with rules_file.open("w") as rules:
                 solvers.add(solver)
                 engine_solvers.add((engine, solver))
 
+        if any(line.startswith("read -verific") or line.startswith("verific") for line in info["script"]):
+            required_tools.add("verific")
+
         required_tools = sorted(required_tools)
 
         print(f".PHONY: {target}", file=rules)