refactor: restore settings through their typed prefs

applyBackup re-derived every key name, type and clamp by hand because
Pref.write was internal to floret-kit. floret-kit now has a typed
MutablePreferences[pref] = value, so a restored value is stored exactly
as its setter would, and a changed range or encoding reaches restore
too.

app/src/test/java/de/jeanlucmakiola/clockula/data/prefs/SettingsPrefsTest.kt

@@ -74,7 +74,7 @@ class SettingsPrefsTest {
             BackupSettings(
                 themeMode = ThemeMode.DARK,
                 dynamicColor = false,
-                defaults = ClockDefaults(snoozeMinutes = 99, volumeRampSeconds = 99),
+                defaults = ClockDefaults(snoozeMinutes = 99, volumeRampSeconds = 99, alarmRingtoneUri = "  "),
                 timerPresets = listOf(5.minutes, 1.minutes, 5.minutes),
             ),
         )
@@ -83,6 +83,7 @@ class SettingsPrefsTest {
         assertThat(prefs.dynamicColor.first()).isFalse()
         assertThat(prefs.currentDefaults().snoozeMinutes).isEqualTo(60)
         assertThat(prefs.currentDefaults().volumeRampSeconds).isEqualTo(60)
+        assertThat(prefs.currentDefaults().alarmRingtoneUri).isNull()
         assertThat(prefs.timerPresets.first()).containsExactly(1.minutes, 5.minutes).inOrder()
     }