Import timestamp and duration by file, not from root (#139)

this fixes a circular import or circular definition problem that we don't fully understand.

Author: gefjon

packages/sdk/src/algebraic_type.ts

@@ -1,4 +1,5 @@
-import { TimeDuration, Timestamp } from '.';
+import { TimeDuration } from './time_duration';
+import { Timestamp } from './timestamp';
 import { ConnectionId } from './connection_id';
 import type BinaryReader from './binary_reader';
 import type BinaryWriter from './binary_writer';