feat(host): vendor PyroWave + minimal Granite subset as crates/pyrowave-sys

Phase 0 of design/pyrowave-codec-plan.md — the opt-in wired-LAN ultra-low-
latency codec. Vendored at upstream 509e4f88 (API 0.4.0, Granite 44362775,
volk + vulkan-headers pins in PUNKTFUNK-VENDOR.txt), pruned to the 6.6 MB
the standalone no-renderer build needs; scripts/vendor-pyrowave.sh
reproduces the tree (a pin bump is protocol-affecting, plan §4.2).

build.rs drives the wrapper CMakeLists (static archives incl. a static
C-API lib upstream only ships shared) + bindgen over pyrowave.h; Linux and
Windows only, empty stub elsewhere (Apple gets a native Metal port, §4.7).
Offline-safe by construction: no network, no system lib, vendored Vulkan
headers — same model as the opus dep (flatpak builder has no network).

Phase-0 validation on .21 (RTX 5070 Ti, driver 610.43.03):
- upstream pyrowave-c-test + interop test (incl. dmabuf/DRM-modifier
  Vulkan<->Vulkan) pass, from the pristine AND the pruned tree
- GPU kernel times at ~1.6 bpp noise: encode/decode 0.090/0.042 ms @800p,
  0.146/0.067 @1080p, 0.226/0.103 @1440p, 0.477/0.201 @4K — order of
  magnitude under NVENC's 1-2 ms retrieve, CBR lands within ~100 B of
  target
- cargo test -p pyrowave-sys green (static link + API-version pin check)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pyrowave-sys/vendor/pyrowave/Granite/vulkan/wsi_pacer.hpp

@@ -0,0 +1,92 @@
+/* Copyright (c) 2017-2026 Hans-Kristian Arntzen
+*
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#pragma once
+
+#include "small_vector.hpp"
+#include <stdint.h>
+
+// Designed for lowest possible latency on fixed rate displays.
+// The GPU workload is expected to be very light and stable (e.g. video decoding).
+class FixedRefreshRatePacer
+{
+public:
+	FixedRefreshRatePacer();
+	~FixedRefreshRatePacer();
+
+	void set_frame_time_ns(uint64_t frame_time);
+	void update_feedback(uint64_t present_id, uint64_t queue_done_ns, uint64_t complete_ns);
+
+	// Sleeps as needed. Should be called before sampling inputs, etc.
+	void begin_frame_submission(uint64_t current_present_id);
+
+	// This frame will not be valid for purposes of statistics.
+	void discard_pacing_statistics(uint64_t present_id);
+
+	// Can avoid some weird interactions with async compute and such.
+	void override_gpu_done_time(uint64_t present_id, uint64_t queue_done_ns);
+
+	void reset();
+
+	struct HistogramStats
+	{
+		double confidence = 0.0;
+		uint64_t last_failure_present_id = 0;
+		uint64_t num_relevant_present_failures = 0;
+	};
+
+	// Debugging.
+	HistogramStats get_current_histogram_stats() const;
+	HistogramStats get_candidate_histogram_stats() const;
+	HistogramStats get_overall_histogram_stats() const;
+	uint64_t get_estimated_present_gap_ns() const;
+	uint64_t get_estimated_cpu_gpu_idle_latency_ns() const;
+	double get_minimum_confidence_for_promotion() const;
+
+private:
+	uint64_t frame_time_ns = 0;
+	uint64_t estimated_present_gap_ns = UINT64_MAX;
+	uint64_t estimated_frame_latency_ns = UINT64_MAX;
+	double minimum_confidence_for_promotion = 0.0;
+
+	struct Feedback
+	{
+		uint64_t present_id;
+		uint64_t frame_submission_ns;
+		uint64_t estimated_complete_ns;
+		uint64_t queue_done_ns;
+		uint64_t complete_ns;
+	};
+
+	Util::SmallVector<Feedback> feedbacks;
+	Feedback last_feedback = {};
+	Feedback find_and_remove_feedback(uint64_t present_id);
+
+	// Don't make the quant interval too narrow, or we won't be able capture statistics well.
+	enum { GapQuantumNS = 250 * 1000, NumHistogramEntries = 64 };
+
+	HistogramStats histogram[NumHistogramEntries];
+	HistogramStats overall;
+
+	void register_present_gap(uint64_t present_id, uint64_t gap_ns, bool success);
+	bool safe_to_lower_gap_to(uint64_t present_id, uint64_t observed_gap_ns, uint64_t to_ns) const;
+};