mem: typed allocation helpers + drop bare malloc/free (Phase 2.2); resolve 0119 as |>-contract clarification

examples/0808-memory-xx-value-routes-through-context-allocator.sx

@@ -15,7 +15,7 @@ Tracer :: struct {
     count: s64;
 
     init :: () -> *Tracer {
-        t : *Tracer = xx malloc(size_of(Tracer));
+        t : *Tracer = xx libc_malloc(size_of(Tracer));
         t.count = 0;
         t
     }
@@ -24,10 +24,10 @@ Tracer :: struct {
 impl Allocator for Tracer {
     alloc_bytes :: (self: *Tracer, size: s64) -> *void {
         self.count += 1;
-        return malloc(size);
+        return libc_malloc(size);
     }
     dealloc_bytes :: (self: *Tracer, ptr: *void) {
-        free(ptr);
+        libc_free(ptr);
     }
 }