chore: release 1.0.3-beta.0 (#146)

Beta release: ships PER-7348 readiness gate (waitForReady before
serialize) via @percy/cli@^1.31.15-beta.0.

Author: Shivanshu-07

percy/version.py

@@ -1 +1 @@
-__version__ = "1.0.2"
+__version__ = "1.0.3-beta.0"