feat(lang): L5 generic records and functions

property Pool<T> { ... }, function first<T>(xs: []T) -> T, map<T, U> over fn
types; a type writes an instance as Pool<Thing>, nested as deep as needed. The
parser names an instance Pool$Thing and remembers its generic and arguments; the
checker takes the generic declarations out, infers a call's type arguments from
its arguments or its result's declared slot, and makes each instance once as an
ordinary record or function, checked like any other. Errors print Pool<Thing>.
An instance keeps its generic's module and export (L3). ludic-fmt keeps type
arguments together while spacing comparisons and shifts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/check/check_index.ludic

@@ -69,6 +69,10 @@ function ck_index() -> void {
 }
 function ck_fn(name: pointer) -> Node { return ck_tab_get(ck_fn_k, ck_fn_v, name) }
 function ck_global(name: pointer) -> Node { return ck_tab_get(ck_gl_k, ck_gl_v, name) }
-function ck_record(name: pointer) -> Node { return ck_tab_get(ck_rec_k, ck_rec_v, name) }
+function ck_record(name: pointer) -> Node {
+  let r = ck_tab_get(ck_rec_k, ck_rec_v, name)
+  if r != null { return r }
+  return gen_record(name)
+}
 function ck_enum(name: pointer) -> Node { return ck_tab_get(ck_en_k, ck_en_v, name) }
 function ck_extern(name: pointer) -> Node { return ck_tab_get(ck_ex_k, ck_ex_v, name) }