add Exn_bt.pp

src/core/exn_bt.ml

@@ -13,6 +13,7 @@ let[@inline] get_callstack n exn =
   make exn bt
 
 let show self = Printexc.to_string (fst self)
+let pp out self = Format.pp_print_string out (show self)
 let[@inline] raise self = Printexc.raise_with_backtrace (exn self) (bt self)
 
 type nonrec 'a result = ('a, t) result

src/core/exn_bt.mli

@@ -22,4 +22,6 @@ val raise : t -> 'a
 val show : t -> string
 (** Simple printing *)
 
+val pp : Format.formatter -> t -> unit
+
 type nonrec 'a result = ('a, t) result