gpu: optimize resourceCache

By keeping all the information in a single map, we avoid multiple
lookups and can switch between frames more easily.

Before ~35us, after ~20us for adding 50 new+old and switching
the frame.

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

gpu/caches_test.go

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import "testing"
+
+func BenchmarkResourceCache(b *testing.B) {
+	offset := 0
+	const N = 100
+
+	cache := newResourceCache()
+	for i := 0; i < b.N; i++ {
+		// half are the same and half updated
+		for k := 0; k < N; k++ {
+			cache.put(offset+k, nullResource{})
+		}
+		cache.frame()
+		offset += N / 2
+	}
+}
+
+type nullResource struct{}
+
+func (nullResource) release() {}