ocaml: phase 6 Option/Result/Bytes extensions (+9 tests, 439 total)

Option: join, to_result, some, none.
Result: value, iter, fold.
Bytes: length, get, of_string, to_string, concat, sub — thin alias of
String (SX has no separate immutable byte type).

Ordering fix: Bytes module placed after String so its closures capture
String in scope. Earlier draft put Bytes before String which made
String.* lookups fail with 'not a record/module' (treated as nullary
ctor).

plans/ocaml-on-sx.md

@@ -399,6 +399,12 @@ _Newest first._
   recognise `!` as the prefix-deref of an application argument, so
   `String.concat "" (List.rev !b)` parses as `(... (deref b))`. Buffer
   uses a ref holding a string list; contents reverses and concats.
+- 2026-05-08 Phase 6 — Option/Result/Bytes extensions (+9 tests, 439
+  total). Option: join, to_result, some, none. Result: value, iter,
+  fold. Bytes: length, get, of_string, to_string, concat, sub (thin
+  alias of String — SX has no separate immutable byte type). Ordering
+  fix: Bytes module placed after String so its closures capture String
+  in scope.
 - 2026-05-08 Phase 6 — `Stack` and `Queue` modules in OCaml (+5 tests,
   430 total). Stack: ref-holding-list LIFO with push/pop/top/length/
   is_empty/clear. Queue: amortised O(1) two-list `(front, back)` queue