feat(lang): functions are values (L2), and render3d takes its scene as callbacks

fn(int, float) -> bool is a type, fn name is any top-level function's value, and a call through
a local, a global, a record field, a slice element, a parameter or a result of a function type
is an indirect call; two function types mix only when equal, a call checks its argument count,
and a value may be null (examples/functions/values.ludic). Job.parallel_for keeps its worker
check.

render3d's scene is registered rather than required by name: r3d_on_draw, r3d_on_casters and
r3d_on_stream_fill (hooks.ludic). The two rendering examples register theirs - and had defined
scene_draw_casters with no parameter while the renderer passed one, which nothing checked.
render3d declares numbers float itself; smooth.ludic is converted to floats and returns when
r3d_init fails instead of running on into a segfault. Noise.* check their argument count (a call
one short crashed the compiler). selfhost-build says why it failed. The migration tool reads a
declared float as evidence. Seed regenerated.

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

tools/migrate/floatinfer.py

@@ -87,6 +87,11 @@ class Program:
         self.uf = UF()
         self.types = {}          # key -> declared type text
         for d in self.all_decls(): self.types[d.key] = d.ty
+        # a declaration that already says float is evidence of its own: code converted earlier
+        # (render3d, once the game had moved) is read as it is written
+        for d in self.all_decls():
+            if d.ty == 'float': self.uf.mark(d.key, 'f', 'declared float')
+            elif d.ty in ('floats', '[]float'): self.uf.mark(('E', d.key), 'f', 'declared floats')
         self.calls = []          # (callee Func, arg index, arg key, node)
         self.bound_args = []     # (call node, arg node, arg key): a float going into a runtime call
         self.bound_rets = {}     # call node id -> key of a runtime result