Constrain package vesions for Python 3.10 (#1003)

A `pip install -r requirements.txt` has started failing for me in Python
3.10 because the latest versions of some transitive dependencies have
dropped support for Python 3.10 (or require Python 3.11+ for their build
environments). Constraining Numpy, Contourpy and Scipy resolves the
problem.

Author: mhucka

requirements.txt

@@ -1,3 +1,9 @@
 absl-py
 cirq-core~=1.0
-numpy>=1.26.0
+
+# Constrain some versions because they dropped support for Python 3.10.
+# Countourpy is pulled in by Matplotlib, which is pulled in by Cirq.
+contourpy<1.3.0; python_version <= '3.10'
+numpy<2.0.0; python_version <= '3.10'
+numpy>=1.26.0; python_version > '3.10'
+scipy<1.15.0; python_version <= '3.10'