build: declare build dependencies in pyproject.toml

setup.py imports grpc_tools at module level (to compile protos at install
time). Without a [build-system] table, pip's isolated build env lacks
grpc_tools and pip install fails before setup() runs. Declare the build
deps explicitly so pip install -e . works under build isolation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jmayank1511

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools>=61", "wheel", "grpcio-tools"]
+build-backend = "setuptools.build_meta"