perf(render): in-place GPU wire arena for move/edit (phase 4, OCS_WIRE_GPU_PATCH)

On a geometry edit the resident set gets a fresh content id, so the batched wire
path (build_wire_buffers) re-emits and re-uploads EVERY wire instance — the whole
buffer even when one line moved. Behind the OCS_WIRE_GPU_PATCH flag (default off,
native only), add a persistent per-entity instance arena: one long-lived
VERTEX|COPY_DST instance buffer + its WireConst storage, with a per-entity slab
table. An in-place edit (move / rotate / scale / colour — same segment count)
becomes a queue.write_buffer of just that entity`s slab.

Scope is deliberately IN-PLACE ONLY. draw_depth_map normalises each entity`s
draw-order z-bias by the block`s entity count, so an Add or Remove re-scales EVERY
entity`s z-bias — which a per-slab patch can`t honour — and a segment-count change
relocates the entity. patch() returns false for any of those (and for mesh-edge /
scissored sets), and the caller falls back to the identical full batched rebuild,
so correctness never rides on the fast path. An adversarial review of an earlier
append/tombstone design surfaced exactly these draw-order hazards; restricting to
in-place removes them while keeping the common interactive-edit win.

The Scene hands the changed handles to the arena via model_wire_gpu_patch,
recorded by try_resident_patch for the Model block and matched by content id in
prepare(); scissored paper viewports and mixed 2D/3D sets keep the batched path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/pipeline/wire_gpu.rs

@@ -383,7 +383,7 @@ fn emit_wire_instances(wire: &WireModel, color: [f32; 4], draw_depth: f32) -> Ve
 /// Native: emit slim per-segment instances (positions + distances + `wire_id`)
 /// plus the one `WireConst` record every segment of this wire shares.
 #[cfg(not(target_arch = "wasm32"))]
-fn emit_wire_native(
+pub(crate) fn emit_wire_native(
     wire: &WireModel,
     wire_id: u32,
     color: [f32; 4],
@@ -432,7 +432,10 @@ fn emit_wire_native(
 /// Looks up a wire's draw-order depth from the per-entity map using the
 /// handle encoded in its `name`. Falls back to 0.0 (transient / preview
 /// wires that carry no document handle).
-fn wire_draw_depth(wire: &WireModel, depth_map: &rustc_hash::FxHashMap<u64, f32>) -> f32 {
+pub(crate) fn wire_draw_depth(
+    wire: &WireModel,
+    depth_map: &rustc_hash::FxHashMap<u64, f32>,
+) -> f32 {
     wire
         .name
         .parse::<u64>()