Update return type and adjust the imports and namespace

The commit updates the return type of filter methods in `Contacts.php` and `Invoices.php` from `static` to explicit class names, for better clarity and stability. It also changes some uses of fully qualified class names in `XeroAuthenticated.php` and `XeroShowAllCommand.php` to uses of `use` statements for better readability. Unnecessary namespace in `XeroShowAllCommand.php` was removed.

src/Console/Commands/XeroShowAllCommand.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace App\Console\Commands;
+namespace Dcblogdev\Xero\Console\Commands;
 
 use Illuminate\Console\Command;
 use Dcblogdev\Xero\Models\XeroToken;
@@ -45,7 +45,6 @@ public function handle()
                     $access_token = Crypt::decryptString($token->access_token);
                 } catch (DecryptException $e) {
                     $access_token = $token->access_token;
-                    $refresh_token = $token->refresh_token;
                 }
 
                 // Split them as a refresh token may not exist...

src/Resources/Contacts.php

@@ -10,7 +10,7 @@ class Contacts extends Xero
 {
     protected array $queryString = [];
 
-    public function filter($key, $value): static
+    public function filter($key, $value): Contacts
     {
         if (! FilterOptions::isValid($key)) {
             throw new InvalidArgumentException("Filter option '$key' is not valid.");

src/Resources/Invoices.php

@@ -10,7 +10,7 @@ class Invoices extends Xero
 {
     protected array $queryString = [];
 
-    public function filter($key, $value): static
+    public function filter($key, $value): Invoices
     {
         if (! FilterOptions::isValid($key)) {
             throw new InvalidArgumentException("Filter option '$key' is not valid.");

src/XeroAuthenticated.php

@@ -4,18 +4,20 @@
 
 use Closure;
 use Dcblogdev\Xero\Facades\Xero;
+use Exception;
+use \Illuminate\Http\Request;
 
 class XeroAuthenticated
 {
     /**
      * Handle an incoming request.
      *
-     * @param \Illuminate\Http\Request $request
-     * @param \Closure $next
+     * @param Request $request
+     * @param Closure $next
      * @return mixed
-     * @throws \Exception
+     * @throws Exception
      */
-    public function handle($request, Closure $next): mixed
+    public function handle(Request $request, Closure $next)
     {
         if (! Xero::isConnected()) {
             return Xero::connect();