feat: Add support for serializing Error causes

pack.js

@@ -896,7 +896,7 @@ extensions = [{
 			target[position++] = 0x65 // 'e' for error
 			target[position++] = 0
 		}
-		pack([ error.name, error.message ])
+		pack([ error.name, error.message, error.cause ])
 	}
 }, {
 	pack(regex, allocateForWrite, pack) {

tests/test.js

@@ -703,6 +703,24 @@ suite('msgpackr basic tests', function() {
 			}
 	})
 
+	test('moreTyesp: Error with causes', function() {
+		const object = {
+			error: new Error('test'),
+			errorWithCause: new Error('test-1', { cause: new Error('test-2')}),
+		}
+		const packr = new Packr({
+			moreTypes: true,
+		})
+
+		const serialized = packr.pack(object)
+		const deserialized = packr.unpack(serialized)
+		assert.equal(deserialized.error.message, object.error.message)
+		assert.equal(deserialized.error.cause, object.error.cause)
+		assert.equal(deserialized.errorWithCause.message, object.errorWithCause.message)
+		assert.equal(deserialized.errorWithCause.cause.message, object.errorWithCause.cause.message)
+		assert.equal(deserialized.errorWithCause.cause.cause, object.errorWithCause.cause.cause)
+	})
+
 	test('structured cloning: self reference', function() {
 		let object = {
 			test: 'string',

unpack.js

@@ -1010,7 +1010,7 @@ currentExtensions[0x42] = (data) => {
 let errors = { Error, TypeError, ReferenceError };
 currentExtensions[0x65] = () => {
 	let data = read()
-	return (errors[data[0]] || Error)(data[1])
+	return (errors[data[0]] || Error)(data[1], { cause: data[2] })
 }
 
 currentExtensions[0x69] = (data) => {