fix(build): resolve :nappletHost benchmark variant via matchingFallbacks

The new plain-AGP :nappletHost library only declares debug/release build
types (unlike the KMP :commons/:quartz libs, which match any build type).
The :amethyst app's `benchmark` build type had no fallback, so Gradle could
not resolve a matching :nappletHost variant for fdroidBenchmark/playBenchmark,
breaking Test/Build CI on main.

Add `matchingFallbacks += "release"` to the benchmark build type so it falls
back to a library's release variant when no benchmark variant exists.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014tzXcqVUcAPhyDDFak4SQ8

amethyst/build.gradle.kts

@@ -212,6 +212,9 @@ android {
         }
         create("benchmark") {
             initWith(getByName("release"))
+            // Plain AGP library deps (e.g. :nappletHost) only declare debug/release build types,
+            // so fall back to their `release` variant when resolving the benchmark build type.
+            matchingFallbacks += "release"
             applicationIdSuffix = ".benchmark"
             versionNameSuffix = "-BENCHMARK"
             resValue("string", "app_name", "@string/app_name_benchmark")