feat(tests): run subdirectory of tests

example: `west test tests/hold-tap` will run all hold-tap tests.

app/run-test.sh

@@ -8,15 +8,24 @@
 if [ -z "$1" ]; then
 	echo "Usage: ./run-test.sh <path to testcase>"
 	exit 1
-elif [ "$1" = "all" ]; then
+fi
+
+path="$1"
+if [ path = "all" ]; then
+	path = "tests"
+fi
+
+testcases=$(find $path -name native_posix.keymap -exec dirname \{\} \;)
+num_cases=$(echo "$testcases" | wc -l)
+if [ $num_cases -gt 1 ]; then
 	echo "" > ./build/tests/pass-fail.log
-	find tests -name native_posix.keymap -exec dirname \{\} \; | xargs -l -P 4 ./run-test.sh
+	echo "$testcases" | xargs -l -P 4 ./run-test.sh
 	err=$?
 	sort -k2 ./build/tests/pass-fail.log
 	exit $err
 fi
 
-testcase="$1"
+testcase="$path"
 echo "Running $testcase:"
 
 west build -d build/$testcase -b native_posix -- -DZMK_CONFIG=$testcase > /dev/null 2>&1