Avoid database access on the main thread when opening the settings

`getUserProfile()` was storing the user profile (DB read, avatar Base64 encoding, DB write) on the caller
dispatcher, i.e. the main thread when called from a presenter, causing glitches in the screen transition.
- Run the whole `getUserProfile()` on the session dispatcher.
- Make `DatabaseSessionStore` main-safe by running the queries on the IO dispatcher.
- Do not refresh the profile twice from the settings screen.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

features/preferences/impl/src/main/kotlin/io/element/android/features/preferences/impl/account/PreferencesAccountPresenter.kt

@@ -40,10 +40,7 @@ class PreferencesAccountPresenter(
     @Composable
     override fun present(): PreferencesAccountState {
         val matrixUser = matrixClient.userProfile.collectAsState()
-        LaunchedEffect(Unit) {
-            // Force a refresh of the profile
-            matrixClient.getUserProfile()
-        }
+        // Note: no need to force a refresh of the profile here, PreferencesRootPresenter, which embeds this presenter, already does it.
         val showLinkNewDevice by remember {
             featureFlagService.isFeatureEnabledFlow(FeatureFlags.QrCodeLogin)
         }.collectAsState(initial = false)