ref: add pymemcache (#61393)

on its own this change does nothing -- I will later be adjusting the
memcache backend to try out the alternative library backing

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requirements-base.txt

@@ -46,6 +46,8 @@ psycopg2-binary>=2.9.7
 PyJWT>=2.4.0
 pydantic>=1.10.9
 python-dateutil>=2.8.2
+pymemcache
+# TODO: once pymemcache is validated, remove python-memcached
 python-memcached>=1.59
 python-u2flib-server>=5.0.0
 fido2>=0.9.2

requirements-dev-frozen.txt

@@ -136,6 +136,7 @@ pycparser==2.21
 pydantic==1.10.9
 pyflakes==3.1.0
 pyjwt==2.4.0
+pymemcache==4.0.0
 pyparsing==3.0.9
 pyrsistent==0.18.1
 pysocks==1.7.1

requirements-frozen.txt

@@ -94,6 +94,7 @@ pycountry==17.5.14
 pycparser==2.21
 pydantic==1.10.9
 pyjwt==2.4.0
+pymemcache==4.0.0
 pyparsing==3.0.9
 pyrsistent==0.18.1
 python-dateutil==2.8.2