Refactor static database connection handling and update synchronization functions

This commit removes hardcoded database connection details from the `fxStaticSyncClientDatabaseConfigs` function, returning an empty array instead. It also refines the `fxStaticSyncConnect` function to utilize `mysqli_init` for improved connection management and introduces a new `fxStaticSyncOpenConnections` function to reuse existing connections. Additionally, the script execution time limit is increased in `sync_static_db.php` to accommodate longer operations.

php/sync_static_db.php

@@ -16,6 +16,8 @@ if (!fxAdminStaticSyncAllowed()) {
     exit;
 }
 
+set_time_limit(300);
+
 function ssEsc($str) {
     return htmlspecialchars((string)$str, ENT_QUOTES, 'UTF-8');
 }