feat(lang): ports - port Clock { ... } in a module, bind Clock { ... } in the app

A port is a record of function values a module calls through
(Clock.now()) without naming the module that answers. A port used and
never bound, a bind missing a required member or naming one the port
lacks, and a second bind are refused; the binder must see the port, and
what it binds is checked from its own file. Reseed.

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

changes/ports.md

@@ -0,0 +1,7 @@
+bump: minor
+type: feature
+**Ports: `port Clock { now: fn() -> int, day: fn() -> int = fn first_day }` in a module and
+`bind Clock { now: fn game_hours }` where the program is put together.** A module asks for what it
+needs through `Clock.now()` without naming - or `uses`-ing - the module that answers. A port used
+and never bound, a bind that leaves out a member with no default, a member the port does not have
+and a second bind are refused; the binder must see the (exported) port.