fix: add exceptiongroup dependency for Python 3.10 compatibility

ROOT CAUSE:
Python 3.10 doesn't have BaseExceptionGroup in builtins.
The exceptiongroup backport package needs to be installed.

CHANGES:
- Added "exceptiongroup>=1.2.0; python_version < '3.11'" to dependencies

IMPACT:
Python 3.10 tests will now pass

FILES MODIFIED:
- pyproject.toml
- uv.lock

Author: peter-luminova

pyproject.toml

@@ -26,6 +26,7 @@ classifiers = [
 ]
 dependencies = [
     "anyio>=4.5",
+    "exceptiongroup>=1.2.0; python_version < '3.11'",
     "httpx>=0.27.1",
     "httpx-sse>=0.4",
     "pydantic>=2.12.0",