feat(repr): add interval info to interval repr

trying this out.  there are a lot of ways to make this more complicated
and some of them might be worth it, but this seems to provide a little
more information with a tiny footprint.

ibis/expr/format.py

@@ -534,6 +534,8 @@ def _fmt_value_negate(op: ops.Negate, *, aliases: Aliases) -> str:
 
 @fmt_value.register
 def _fmt_value_literal(op: ops.Literal, **_: Any) -> str:
+    if isinstance(op.dtype, dt.Interval):
+        return f"{op.value} {op.dtype.unit}"
     return repr(op.value)