Add __toString implementation across value objects and update tests

- Implemented `__toString` in `DateTimeType`, `IntType`, `FloatType`, `StrType`, and `UndefinedType`.
- Extended interfaces to mandate `__toString` declaration.
- Enhanced unit tests to validate `__toString` behavior for all value objects.
- Introduced architectural tests to ensure all value objects and interfaces define `__toString`.

Author: georgedeploy

src/Abstract/DateTime/DateTimeType.php

@@ -111,4 +111,9 @@ public static function getFormat(): string
     {
         return static::FORMAT;
     }
+
+    public function __toString(): string
+    {
+        return $this->toString();
+    }
 }

src/Abstract/DateTime/DateTimeTypeInterface.php

@@ -18,4 +18,6 @@ public static function fromDateTime(DateTimeImmutable $value): static;
     public function toString(): string;
 
     public static function fromString(string $value): static;
+
+    public function __toString(): string;
 }

src/Abstract/Float/FloatType.php

@@ -27,4 +27,9 @@ public function toString(): string
     {
         return (string) $this->value();
     }
+
+    public function __toString(): string
+    {
+        return $this->toString();
+    }
 }

src/Abstract/Float/FloatTypeInterface.php

@@ -16,4 +16,6 @@ public static function fromFloat(float $value): static;
     public function toString(): string;
 
     public static function fromString(string $value): static;
+
+    public function __toString(): string;
 }

src/Abstract/Integer/IntType.php

@@ -29,4 +29,9 @@ public function toString(): string
     {
         return (string) $this->value();
     }
+
+    public function __toString(): string
+    {
+        return $this->toString();
+    }
 }

src/Abstract/Integer/IntTypeInterface.php

@@ -16,4 +16,6 @@ public static function fromInt(int $value): static;
     public function toString(): string;
 
     public static function fromString(string $value): static;
+
+    public function __toString(): string;
 }

src/Abstract/String/StrType.php

@@ -13,4 +13,9 @@ public function toString(): string
     {
         return $this->value();
     }
+
+    public function __toString(): string
+    {
+        return $this->toString();
+    }
 }

src/Abstract/String/StrTypeInterface.php

@@ -14,4 +14,6 @@ public function value(): string;
     public static function fromString(string $value): static;
 
     public function toString(): string;
+
+    public function __toString(): string;
 }

src/Abstract/Undefined/UndefinedType.php

@@ -35,4 +35,12 @@ public function value(): void
     {
         throw new UndefinedTypeException('Undefined type has no value.');
     }
+
+    /**
+     * @throws UndefinedTypeException
+     */
+    public function __toString(): string
+    {
+        throw new UndefinedTypeException('Undefined type cannot be converted to string.');
+    }
 }

src/Abstract/Undefined/UndefinedTypeInterface.php

@@ -14,4 +14,6 @@ public static function create(): static;
     public function value(): void;
 
     public function toString(): void;
+
+    public function __toString(): string;
 }