green(reify): RecvResult/TryResult channel result types over reify

REIFY Phase 3.1. Add RecvResult($T) and TryResult($T) to meta.sx as
type-fns over reify (value-or-closed; value-or-empty-or-closed). They
need NO new compiler machinery — reify-of-a-literal in a type-fn body is
exactly the Phase 1 path — so the channel result types are pure sx
library code. examples/0617 green (both construct + match, incl.
payload-less .closed / .empty). Suite green (673 examples, 447 unit).

make_enum(variants) (3.2) and type_info (2.2) remain — both blocked on a
generalized reify reader (reifyType currently AST-walks a literal
TypeInfo). Plan/checkpoint updated.

examples/expected/0617-comptime-reify-recvresult.exit

@@ -0,0 +1 @@
+0

examples/expected/0617-comptime-reify-recvresult.stderr

@@ -0,0 +1 @@
+

examples/expected/0617-comptime-reify-recvresult.stdout

@@ -0,0 +1,4 @@
+recv value 42
+recv closed
+try value 7
+try empty