refactor(config): add EnumResolver for cache-backed enum resolution and extend DockerSecretsResolver with caching

- Introduce `EnumResolver` to centralize and cache enum value conversions.
- Enhance `DockerSecretsResolver` with result caching to avoid redundant file reads and improve performance.
- Update `Environment` to integrate `EnumResolver` for enriched enum resolution support and improved maintainability.
- Adjust unit tests to validate caching mechanisms and error handling improvements.

tests/Unit/Framework/Config/EnvironmentTest.php

@@ -583,6 +583,89 @@ describe('Environment', function () {
             unlink($dbPasswordPath);
             unlink($apiKeyPath);
         });
+
+        it('uses Docker secret when variable is set to empty string', function () {
+            // Create temporary Docker secret file
+            $secretPath = '/tmp/docker_secret_test';
+            file_put_contents($secretPath, 'secret_from_file');
+
+            $env = new Environment([
+                'REDIS_PASSWORD' => '',  // Empty string
+                'REDIS_PASSWORD_FILE' => $secretPath,
+            ], $this->dockerSecretsResolver);
+
+            $value = $env->get('REDIS_PASSWORD');
+
+            // Docker Secret should override empty string
+            expect($value)->toBe('secret_from_file');
+
+            // Cleanup
+            unlink($secretPath);
+        });
+
+        it('returns empty string when variable is empty and no Docker secret exists', function () {
+            $env = new Environment([
+                'REDIS_PASSWORD' => '',  // Empty string, no FILE
+            ], $this->dockerSecretsResolver);
+
+            $value = $env->get('REDIS_PASSWORD');
+
+            // Empty string should be returned when explicitly set
+            expect($value)->toBe('');
+        });
+
+        it('caches Docker secret resolution results', function () {
+            // Create temporary Docker secret file
+            $secretPath = '/tmp/docker_secret_test_caching';
+            file_put_contents($secretPath, 'cached_secret_value');
+
+            $env = new Environment([
+                'DB_PASSWORD_FILE' => $secretPath,
+            ], $this->dockerSecretsResolver);
+
+            // First call - should read from file
+            $value1 = $env->get('DB_PASSWORD');
+            expect($value1)->toBe('cached_secret_value');
+
+            // Modify file content (should not affect cached value)
+            file_put_contents($secretPath, 'modified_secret_value');
+
+            // Second call - should use cache, not re-read file
+            $value2 = $env->get('DB_PASSWORD');
+            expect($value2)->toBe('cached_secret_value');
+
+            // Cleanup
+            unlink($secretPath);
+        });
+
+        it('caches enum conversion results', function () {
+            // Create a test enum
+            if (!enum_exists('TestEnum')) {
+                eval('enum TestEnum: string { case FOO = "foo"; case BAR = "bar"; }');
+            }
+
+            $env = new Environment([
+                'APP_ENV' => 'foo',
+            ], $this->dockerSecretsResolver);
+
+            $default = TestEnum::BAR;
+
+            // First call - should convert
+            $enum1 = $env->getEnum('APP_ENV', TestEnum::class, $default);
+            expect($enum1)->toBe(TestEnum::FOO);
+
+            // Second call to same instance should use cache
+            $enum2 = $env->getEnum('APP_ENV', TestEnum::class, $default);
+            expect($enum2)->toBe(TestEnum::FOO);
+            expect($enum1)->toBe($enum2);
+
+            // Different enum class should have different cache entry
+            if (!enum_exists('AnotherTestEnum')) {
+                eval('enum AnotherTestEnum: string { case FOO = "foo"; case BAR = "bar"; }');
+            }
+            $enum3 = $env->getEnum('APP_ENV', AnotherTestEnum::class, AnotherTestEnum::BAR);
+            expect($enum3)->toBe(AnotherTestEnum::FOO);
+        });
     });
 
     describe('Edge Cases', function () {