perf(pyrowave): pool encoder scratch buffers + fix client parser O(n²) — lift the 2.5 Gbps wall

Real-world PyroWave streaming maxed ~2.5 Gbps with sagging fps while raw
transport does 4.8. Root-caused to serial per-frame paths at BOTH ends
(the transport was never the limit); this fixes the two dominant ones.

Host (vendored shim, patch 0004): pyrowave_encoder_encode_gpu_synchronous
allocated four Vulkan buffers (meta + bitstream, Device + CachedHost) on
EVERY frame. At 240 fps with MB-scale bitstreams that per-frame allocator
churn stalled the encode itself. Pool them on the encoder and reuse across
frames (recreate only on a size grow); the sizes are session-fixed, so it
is pure reuse after frame 1. On an RTX 4090 the 5120x1440 submit+fence-wait
drops ~15 ms -> ~1 ms, i.e. the host serial ceiling goes 64 -> 1025 fps
(444+HDR 44 -> 614). Safe under the synchronous encode model; re-validated
by pyrowave_win_smoke (Windows) and pyrowave_smoke/_444 (Linux). Applies to
both host encoder paths (they share the shim).

Client (Apple Metal decoder): WaveletBitstream.parse reserved the payload
buffer per packet (reserveCapacity(count + words), an exact realloc each of
~3000 packets/frame => O(n²)) and copied word-by-word. Reserve once up
front and memcpy each packet's coefficients in one shot (all Apple
platforms are little-endian, so the wire's LE u32s land verbatim; memcpy is
alignment-free). 5.44 ms -> 0.055 ms per 1.44 MB frame (25x); byte-identical
(parser unit tests + golden-frame PSNR unchanged).

Also:
- native.rs: PUNKTFUNK_PYROWAVE_MAX_MBPS caps PyroWave's open-loop Automatic
  bitrate pin for hosts on a constrained link (unset => no cap; an explicit
  client rate bypasses it). The pin is all-intra + ABR-off, so at a high
  pixel rate it can outrun the fabric (4:4:4+HDR 5120x1440@240 pins ~5.3
  Gbps, over a 5 GbE link) and the overshoot just becomes loss.
- pf-encode caps(): report the real opened chroma instead of a hardcoded
  4:2:0 default, so a genuine 4:4:4 session no longer trips the spurious
  "encoder chroma disagrees with the negotiated Welcome" warn. Also fix a
  latent Windows reset() that rebuilt at 4:2:0 for a 4:4:4 session.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/pyrowave-sys/vendor/pyrowave/pyrowave_c.cpp

@@ -799,6 +799,10 @@ struct pyrowave_encoder_opaque
 	Fence queued_fence;
 	BufferHandle queued_meta;
 	BufferHandle queued_bitstream;
+	// PUNKTFUNK: the GPU-side twins of queued_meta/queued_bitstream, pooled on the encoder so
+	// the encode path reuses them across frames instead of allocating four buffers per frame.
+	BufferHandle queued_meta_gpu;
+	BufferHandle queued_bitstream_gpu;
 	ChromaSubsampling chroma = {};
 	int width = 0;
 	int height = 0;
@@ -936,41 +940,49 @@ pyrowave_encoder_encode_gpu_synchronous(pyrowave_encoder encoder,
 
 	device->next_frame_context();
 
-	BufferCreateInfo bufinfo = {};
-	bufinfo.usage = VK_BUFFER_USAGE_STORAGE_BUFFER_BIT |
-	                VK_BUFFER_USAGE_TRANSFER_DST_BIT |
-	                VK_BUFFER_USAGE_TRANSFER_SRC_BIT;
-
-	bufinfo.size = encoder->encoder.get_meta_required_size();
-	bufinfo.domain = BufferDomain::CachedHost;
-	encoder->queued_meta = device->create_buffer(bufinfo);
-
-	if (!encoder->queued_meta)
-		return PYROWAVE_ERROR_OUT_OF_HOST_MEMORY;
-
-	bufinfo.domain = BufferDomain::Device;
-	auto queued_meta_gpu = device->create_buffer(bufinfo);
-
-	if (!queued_meta_gpu)
-		return PYROWAVE_ERROR_OUT_OF_DEVICE_MEMORY;
-
 	auto target_bitstream_size = rate_control->maximum_bitstream_size & ~VkDeviceSize(3u);
 
 	// Check for bogus sizes.
 	if (target_bitstream_size > UINT32_MAX || target_bitstream_size == 0)
 		return PYROWAVE_ERROR_INVALID_ARGUMENT;
 
-	bufinfo.size = target_bitstream_size + encoder->encoder.get_meta_required_size();
-	bufinfo.domain = BufferDomain::CachedHost;
-	encoder->queued_bitstream = device->create_buffer(bufinfo);
+	const VkDeviceSize meta_size = encoder->encoder.get_meta_required_size();
+	const VkDeviceSize bitstream_size = target_bitstream_size + meta_size;
 
-	if (!encoder->queued_bitstream)
+	// PUNKTFUNK: pool the four scratch buffers on the encoder and only (re)create one when a
+	// larger size is needed. Upstream allocated all four (meta + bitstream, each Device +
+	// CachedHost) on every call; at streaming rates (240 fps, MB-scale bitstreams) that
+	// allocator churn dominated the per-frame CPU cost. The sizes are effectively constant per
+	// session (fixed resolution + a pinned bitrate budget), so after the first frame these are
+	// pure reuse. The synchronous encode model (packetize()/compute_num_packets() wait the
+	// fence before the next encode reuses a buffer) guarantees no in-flight GPU access to a
+	// buffer we hand back, and holding the handles keeps next_frame_context() from recycling
+	// them.
+	BufferCreateInfo bufinfo = {};
+	bufinfo.usage = VK_BUFFER_USAGE_STORAGE_BUFFER_BIT |
+	                VK_BUFFER_USAGE_TRANSFER_DST_BIT |
+	                VK_BUFFER_USAGE_TRANSFER_SRC_BIT;
+
+	auto ensure_buffer = [&](BufferHandle &handle, VkDeviceSize size, BufferDomain domain) -> bool {
+		if (!handle || handle->get_create_info().size < size)
+		{
+			bufinfo.size = size;
+			bufinfo.domain = domain;
+			handle = device->create_buffer(bufinfo);
+		}
+		return bool(handle);
+	};
+
+	auto &queued_meta_gpu = encoder->queued_meta_gpu;
+	auto &queued_bitstream_gpu = encoder->queued_bitstream_gpu;
+
+	if (!ensure_buffer(encoder->queued_meta, meta_size, BufferDomain::CachedHost))
 		return PYROWAVE_ERROR_OUT_OF_HOST_MEMORY;
-
-	bufinfo.domain = BufferDomain::Device;
-	auto queued_bitstream_gpu = device->create_buffer(bufinfo);
-
-	if (!queued_bitstream_gpu)
+	if (!ensure_buffer(queued_meta_gpu, meta_size, BufferDomain::Device))
+		return PYROWAVE_ERROR_OUT_OF_DEVICE_MEMORY;
+	if (!ensure_buffer(encoder->queued_bitstream, bitstream_size, BufferDomain::CachedHost))
+		return PYROWAVE_ERROR_OUT_OF_HOST_MEMORY;
+	if (!ensure_buffer(queued_bitstream_gpu, bitstream_size, BufferDomain::Device))
 		return PYROWAVE_ERROR_OUT_OF_DEVICE_MEMORY;
 
 	Encoder::BitstreamBuffers bitstream_buffers = {};