render3d: place_rec.ludic, the one encoder and decoder of a baked placement

prec_put / prec_get / prec_size (Physics' spec): PREC_FULL, 12 bytes, for trees, boulders and stones
(u16 x, z in 1/65536 of the chunk; u16 y in cm above y_base; u8 scale over the kind's lo..hi, yaw, seed,
wind), and PREC_PACKED, 7 bytes, for the stream kinds (56 bits, least significant first: x 12, z 12,
y 12 in cm, scale 6, yaw 6, seed 4, wind 4). An encode takes the cell a value falls in, a decode its
centre, so a round trip is stable; a record is read from a []byte at an offset, never a pointer.
stream_emit_baked and layer_chunk_put take (recs, at, fmt) and decode through it; the earlier sb7_*
pair is gone.

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

packages/ludic.render3d/env.ludic

@@ -829,6 +829,7 @@ export state Render3dState {
   ter_ortho_tex: int = 0            # a photograph of the same window, draped with distance
   ter_carpet: int = 0               # the distant-grass carpet (carpet_bake), 0 = none
   ter_shadow_tex: int = 0           # height-field sun shadow: R32F, the lowest lit height
+  sb_rec: floats = floats(8)        # one decoded baked record, reused (stream_baked.ludic)
   tt_dir: string = ""               # terrain_tiles_to: where a map's tiles are written ("" keeps the whole copies)
   tt_key: string = ""
   tt_file: pointer = null           # the tiles' file, open for reading (terrain_tiles.ludic)