Os.heap_bytes: the heap without the renderer; string_temps reads it

Vk.heap_bytes pulled the Vk module - and on lang/uifree the GL window path - into a plain program,
which then failed to link (_cgl_offscreen, lgl_GetError). Os.heap_bytes is malloc_zone_statistics
through a weak reference (0 where there is none, and on Windows). Reseeded. Docs for it and for
Json.free / Json.free_all.

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

docs/language/json/json-free.md

@@ -0,0 +1,25 @@
+---
+id: json-free
+name: Json.free
+category: json
+kind: namespace-method
+tokens: Json.free
+sig: Json.free(value) -> void
+tip: Give back a parsed tree's nodes; its strings stay.
+order: 3
+ns: Json
+member: free
+---
+
+Gives back every node and list of a tree <a href="json-parse"><code>Json.parse</code></a> made, once what it describes has been built. Ludic has no garbage collector, so a tree read and dropped is otherwise kept for as long as the program runs. The tree's strings stay, because a reader may keep a name it took out of it; when nothing was kept, <a href="json-free_all"><code>Json.free_all</code></a> gives those back too. Only for a parsed tree: one put together by hand may share a node or hold a literal.
+
+```ludic
+program Free {
+  entry {
+    let doc = Json.parse("{\"hp\": 3}")
+    let hp = value_as_int(value_get(doc, "hp"))
+    Json.free(doc)
+    print(hp)
+  }
+}
+```

docs/language/json/json-free_all.md

@@ -0,0 +1,26 @@
+---
+id: json-free_all
+name: Json.free_all
+category: json
+kind: namespace-method
+tokens: Json.free_all
+sig: Json.free_all(value) -> void
+tip: Give back a parsed tree whole, strings and keys included.
+order: 4
+ns: Json
+member: free_all
+---
+
+<a href="json-free"><code>Json.free</code></a> and every string value and object key the parser made as well: for a reader that copied whatever it keeps (<code>s[0 .. len(s)]</code>), so the whole document goes. A text read, parsed and let go this way leaves nothing behind.
+
+```ludic
+program FreeAll {
+  entry {
+    let doc = Json.parse("{\"name\": \"camp\"}")
+    let s = value_as_str(value_get(doc, "name"))
+    let name = s[0 .. len(s)]
+    Json.free_all(doc)
+    print(name)
+  }
+}
+```