Set minimum python version to 3.7; add support for Python 3.13

[parthea]

See

google-cloud-python-happybase/setup.py

Lines 43 to 49 in 191fa16

	"Programming Language :: Python :: 2",
	"Programming Language :: Python :: 2.7",
	"Programming Language :: Python :: 3",
	"Programming Language :: Python :: 3.4",
	"Programming Language :: Python :: 3.5",
	"Programming Language :: Python :: 3.6",
	"Programming Language :: Python :: 3.7",