feat(android): streaming cache budget and a hardware decoding switch

- Settings > Storage chooses the streaming cache's budget, 1 to 16 GiB,
  and shows what it holds against it. The bridge gains
  set_stream_cache_budget, which the next connection is built with and
  an open one evicts down to at once. Android keeps the choice in its own
  settings, like the desktop keeps it in desktop.json, and tells the
  engine as it is created. Unset stays at the shared 4 GiB default.
- Settings > Playback can turn hardware decoding off for a device whose
  decoder shows green or torn frames. pstr_mpv sets hwdec before each
  loadfile, so it applies from the next episode.

android/app/src/main/java/io/narl/protonstream/native/NativeRuntime.kt

@@ -1,6 +1,7 @@
 package io.narl.protonstream.native
 
 import android.content.Context
+import io.narl.protonstream.settings.SettingsStore
 import java.io.File
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
@@ -56,5 +57,9 @@ object NativeRuntime {
     }
 
     private fun createEngine(): AndroidEngine =
-        AndroidEngine(paths(), KeystoreSecretStore(appContext))
+        AndroidEngine(paths(), KeystoreSecretStore(appContext)).apply {
+            // The budget is Android's setting, so the engine starts on the
+            // default and is told the chosen one before anything streams.
+            setStreamCacheBudget(SettingsStore.gibToBytes(SettingsStore(appContext).cacheBudgetGib))
+        }
 }