deps: bump vgi-rpc 0.20.0 -> 0.20.3

Raise the floor to >=0.20.3 and update the lock. Patch-level bump; full test
suite (1952 passed), ruff, and mypy all clean against the new version.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: rustyconover

pyproject.toml

@@ -26,7 +26,7 @@ dependencies = [
     "pyarrow",
     "typer>=0.9",
     "platformdirs",
-    "vgi-rpc>=0.20.0",
+    "vgi-rpc>=0.20.3",
     "httpx>=0.24",
 ]