move core::pdu and core::state_res into core::matrix::

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/matrix/pdu/tests.rs

@@ -0,0 +1,17 @@
+use super::Count;
+
+#[test]
+fn backfilled_parse() {
+	let count: Count = "-987654".parse().expect("parse() failed");
+	let backfilled = matches!(count, Count::Backfilled(_));
+
+	assert!(backfilled, "not backfilled variant");
+}
+
+#[test]
+fn normal_parse() {
+	let count: Count = "987654".parse().expect("parse() failed");
+	let backfilled = matches!(count, Count::Backfilled(_));
+
+	assert!(!backfilled, "backfilled variant");
+}