Fix: Correct pydantic version range (bytes fields are broken with pydantic<=2.8).

The ser_json_bytes, val_json_bytes we rely on isn't introduced till 2.9.

In old versions B64 encoded bytes fields are getting ascii decoded.
- Users will see different formats of bytes depending on pydantic version.
- The api fails when you send back badly coded bytes (inline_blob, thought_signature).

It's possible to fix it to mostly work with older versions, but definitely not trivial to get **identical** behavior.

PiperOrigin-RevId: 825591037

Author: MarkDaoust

pyproject.toml

@@ -29,7 +29,7 @@ dependencies = [
     "anyio>=4.8.0, <5.0.0",
     "google-auth>=2.14.1, <3.0.0",
     "httpx>=0.28.1, <1.0.0",
-    "pydantic>=2.0.0, <3.0.0",
+    "pydantic>=2.9.0, <3.0.0",
     "requests>=2.28.1, <3.0.0",
     "tenacity>=8.2.3, <9.2.0",
     "websockets>=13.0.0, <15.1.0",