refactor(anthropic-vertex): move SDK runtime to plugin (#71174)

* refactor(anthropic-vertex): move sdk runtime to plugin

* fix(anthropic-vertex): stage provider runtime deps

* fix(anthropic-vertex): reuse stream factory wrapper

package.json

@@ -1581,7 +1581,6 @@
   },
   "dependencies": {
     "@agentclientprotocol/sdk": "0.19.1",
-    "@anthropic-ai/vertex-sdk": "^0.16.0",
     "@clack/prompts": "^1.2.0",
     "@lydell/node-pty": "1.2.0-beta.12",
     "@mariozechner/pi-agent-core": "0.70.2",