feat: tag derivation from ClaML metadata + validity

tests/tags_tests.rs

@@ -0,0 +1,20 @@
+use alpha_id::model::IcdMeta;
+use alpha_id::tags::tags_for;
+
+#[test]
+fn billable_when_para295_is_p_and_valid() {
+    let mut m = IcdMeta::default();
+    m.para295 = "P".into();
+    m.chapter = "01".into();
+    let t = tags_for(&m, true);
+    assert!(t.billable);
+    assert!(t.valid);
+    assert_eq!(t.chapter, "01");
+}
+
+#[test]
+fn not_billable_when_para295_is_v() {
+    let mut m = IcdMeta::default();
+    m.para295 = "V".into();
+    assert!(!tags_for(&m, true).billable);
+}