ocaml: phase 1+3 record type declarations (+3 tests, 447 total)

type r = { x : int; mutable y : string } parses to
(:type-def-record NAME PARAMS FIELDS) with FIELDS each (NAME) or
(:mutable NAME). Parser dispatches on { after = to parse field list.
Field-type sources are skipped (HM registration TBD). Runtime no-op
since records already work as dynamic dicts.

lib/ocaml/eval.sx

@@ -780,6 +780,7 @@
                           (set! env (ocaml-env-extend env mname mod-val))
                           (set! result (merge result (dict mname mod-val))))))))
                 ((= tag "type-def") nil)
+                ((= tag "type-def-record") nil)
                 ((= tag "exception-def") nil)
                 ((= tag "module-type-def") nil)
                 ((= tag "open")
@@ -962,6 +963,10 @@
                   ;; exception E [of T] — purely declarative; raise+match
                   ;; already work on tagged ctor values.
                   nil)
+                ((= tag "type-def-record")
+                  ;; type r = { x : T; y : T } — runtime no-op; records
+                  ;; are already dynamic dicts.
+                  nil)
                 ((= tag "module-type-def")
                   ;; module type S = sig … end — no-op at runtime.
                   nil)