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/settings/SettingsStore.kt

@@ -20,9 +20,34 @@ class SettingsStore(context: Context) {
         get() = preferences.getBoolean(KEY_BACKGROUND_AUDIO, true)
         set(value) { preferences.edit().putBoolean(KEY_BACKGROUND_AUDIO, value).apply() }
 
-    private companion object {
-        const val NAME = "proton_stream_settings"
-        const val KEY_WIFI_ONLY = "wifi_only"
-        const val KEY_BACKGROUND_AUDIO = "background_audio"
+    /**
+     * Whether mpv may decode in hardware. Off is the way out for a device whose
+     * MediaCodec decoder shows green or torn frames; it costs battery, so it is
+     * on unless the viewer turns it off. Read at each load, so a change applies
+     * from the next file.
+     */
+    var hardwareDecoding: Boolean
+        get() = preferences.getBoolean(KEY_HARDWARE_DECODING, true)
+        set(value) { preferences.edit().putBoolean(KEY_HARDWARE_DECODING, value).apply() }
+
+    /** The streaming cache's budget, in GiB. See [CACHE_BUDGET_CHOICES]. */
+    var cacheBudgetGib: Int
+        get() = preferences.getInt(KEY_CACHE_BUDGET_GIB, DEFAULT_CACHE_BUDGET_GIB)
+        set(value) { preferences.edit().putInt(KEY_CACHE_BUDGET_GIB, value).apply() }
+
+    companion object {
+        /** The desktop's range, in the steps a phone's storage is bought in. */
+        val CACHE_BUDGET_CHOICES = listOf(1, 2, 4, 8, 16)
+
+        /** `DiskCacheConfig::DEFAULT_BUDGET_BYTES`, so an unset choice changes nothing. */
+        const val DEFAULT_CACHE_BUDGET_GIB = 4
+
+        fun gibToBytes(gib: Int): ULong = gib.toULong() * 1024uL * 1024uL * 1024uL
+
+        private const val NAME = "proton_stream_settings"
+        private const val KEY_WIFI_ONLY = "wifi_only"
+        private const val KEY_BACKGROUND_AUDIO = "background_audio"
+        private const val KEY_HARDWARE_DECODING = "hardware_decoding"
+        private const val KEY_CACHE_BUDGET_GIB = "cache_budget_gib"
     }
 }