Add type ordering tests for Duration and Stretch.

Also improves testing for other types.

qiskit/circuit/classical/types/ordering.py

@@ -232,7 +232,9 @@ def _uint_cast(from_: Uint, to_: Uint, /) -> CastKind:
     (Float, Float): lambda _a, _b, /: CastKind.EQUAL,
     (Float, Uint): lambda _a, _b, /: CastKind.DANGEROUS,
     (Float, Bool): lambda _a, _b, /: CastKind.DANGEROUS,
+    (Duration, Duration): lambda _a, _b, /: CastKind.EQUAL,
     (Duration, Stretch): lambda _a, _b, /: CastKind.IMPLICIT,
+    (Stretch, Stretch): lambda _a, _b, /: CastKind.EQUAL,
 }