Os.platform/arch uname once; render3d primes a new buffer's Metal buffer

lp_os_platform and lp_os_arch malloc'd 8 KB per call (the uname buffer) and kept none of it:
string_temps now asks both every round, 327 MB over 20,000 before, 0 after. Reseeded. render3d:
MoltenVK made a mapped buffer's MTLBuffer at its first bind (fn_gvk_draw +4 blocks in the boat
window); gvk_buf_reserve queues it and the next frame's command buffer copies 4 bytes out of it.

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

packages/ludic.render3d/env.ludic

@@ -691,6 +691,11 @@ export state Render3dState {
   stream_walks: int = 0          # streams that walked their whole ring this frame
   stream_debug_n: int = 0
   stream_scratch: floats = null
+  gvk_prime_b: words = null        # buffers made since the frame began, read once so MoltenVK makes their
+  gvk_prime_h: []long = null       # Metal buffers now (gvk_prime), and their handles
+  gvk_prime_n: int = 0
+  gvk_prime_dst: long = 0          # the 64 bytes those reads land in
+  gvk_prime_mem: long = 0
   stream_loose: Chunk = null     # the record for a chunk no stream's cache can keep this walk
   stream_deadline: long = 0
   gsl_on: bool = false              # slInit succeeded: the interposer is the loader, the plugins are in