feat(core): improve in-memory validation, FatturaPA detection coverage, and published type compatibility

ts/index.ts

@@ -144,11 +144,12 @@ export function validateXml(
     const validator = ValidatorFactory.createValidator(xml);
     return validator.validate(level);
   } catch (error) {
+    const errorMessage = error instanceof Error ? error.message : String(error);
     return {
       valid: false,
       errors: [{
         code: 'VAL-ERROR',
-        message: `Validation error: ${error.message}`
+        message: `Validation error: ${errorMessage}`
       }],
       level
     };