Derive mode from DSN function

- Add headers in all files
- Minor field name changes

tests/unit/DocumentExceptionTest.php

@@ -1,4 +1,10 @@
 <?php
+/**
+ * @author Daniel J. Summers <daniel@bitbadger.solutions>
+ * @license MIT
+ */
+
+declare(strict_types=1);
 
 namespace Test\Unit;
 
@@ -13,7 +19,7 @@ use PHPUnit\Framework\TestCase;
 #[TestDox('Document Exception (Unit tests)')]
 class DocumentExceptionTest extends TestCase
 {
-    public function testConstructorSucceedsWithCodeAndPriorException()
+    public function testConstructorSucceedsWithCodeAndPriorException(): void
     {
         $priorEx = new Exception('Uh oh');
         $ex = new DocumentException('Test Exception', 17, $priorEx);
@@ -23,7 +29,7 @@ class DocumentExceptionTest extends TestCase
         $this->assertSame($priorEx, $ex->getPrevious(), 'Prior exception not filled properly');
     }
 
-    public function testConstructorSucceedsWithoutCodeAndPriorException()
+    public function testConstructorSucceedsWithoutCodeAndPriorException(): void
     {
         $ex = new DocumentException('Oops');
         $this->assertNotNull($ex, 'The exception should not have been null');
@@ -32,14 +38,14 @@ class DocumentExceptionTest extends TestCase
         $this->assertNull($ex->getPrevious(), 'Prior exception should have been null');
     }
 
-    public function testToStringSucceedsWithoutCode()
+    public function testToStringSucceedsWithoutCode(): void
     {
         $ex = new DocumentException('Test failure');
         $this->assertEquals("BitBadger\PDODocument\DocumentException: Test failure\n", "$ex",
             'toString not generated correctly');
     }
 
-    public function testToStringSucceedsWithCode()
+    public function testToStringSucceedsWithCode(): void
     {
         $ex = new DocumentException('Oof', -6);
         $this->assertEquals("BitBadger\PDODocument\DocumentException: [-6] Oof\n", "$ex",