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>

packages/ludic.render3d/stream.ludic

@@ -233,7 +233,7 @@ function stream_update(s: Stream, cam_x: float, cam_z: float) -> void {
               c.key = key
               s.cur = c
               let t0 = gl_now_us()
-              stream_fill(s, cx, cz, band)
+              r3d_stream_fill(s, cx, cz, band)
               let dt = gl_now_us() - t0
               stream_us_gen = stream_us_gen + dt
               prof_chunk(s.kind, band, c.count, dt)