chore: remove python 3.9 support from pyproject.toml and update target version to 3.10 (google#131)

Author: DeanChensj

pyproject.toml

@@ -5,7 +5,7 @@
 name = "google-adk-community"
 description = "Agent Development Kit Community Repo"
 readme = "README.md"
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 license = { file = "LICENSE" }
 authors = [{ name = "Google LLC", email = "googleapis-packages@google.com" }]
 classifiers = [ # List of https://pypi.org/classifiers/
@@ -14,7 +14,6 @@ classifiers = [ # List of https://pypi.org/classifiers/
   "Intended Audience :: Science/Research",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
@@ -102,7 +101,7 @@ asyncio_mode = "auto"
 
 
 [tool.mypy]
-python_version = "3.9"
+python_version = "3.10"
 exclude = "tests/"
 plugins = ["pydantic.mypy"]
 # Start with non-strict mode, and swtich to strict mode later.