fix: Release cached samplers before WGPU shutdown

SamplerCache singleton never released samplers, causing device to retain
references at shutdown. Add clear() method and call before fixture cleanup.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/gpu/sampler_cache.h b/src/gpu/sampler_cache.h
index 0f012a8..5df3958 100644
--- a/src/gpu/sampler_cache.h
+++ b/src/gpu/sampler_cache.h
@@ -58,4 +58,11 @@ public:
     return {WGPUAddressMode_ClampToEdge, WGPUAddressMode_ClampToEdge,
             WGPUFilterMode_Linear, WGPUFilterMode_Linear, 1};
   }
+
+  void clear() {
+    for (auto& pair : cache_) {
+      wgpuSamplerRelease(pair.second);
+    }
+    cache_.clear();
+  }
 };