feat: restore Assignable for backward compatibility

.changeset/odd-tips-yawn.md

@@ -10,7 +10,7 @@
 "@near-js/providers": major
 "@near-js/signers": minor
 "@near-js/transactions": minor
-"@near-js/types": major
+"@near-js/types": minor
 "@near-js/utils": major
 "@near-js/wallet-account": minor
 ---

packages/types/src/assignable.ts

@@ -0,0 +1,8 @@
+/* DEPRECATED - backward compatibility only */
+export abstract class Assignable {
+    constructor(properties: any) {
+        Object.keys(properties).map((key: any) => {
+            (this as any)[key] = properties[key];
+        });
+    }
+}

packages/types/src/index.ts

@@ -1,3 +1,4 @@
+export * from './assignable';
 export * from './enum';
 export * from './errors';
 export * from './provider';