Use f-strings consistently in engine_client.py helpers (#5037)
Use f-strings consistently in engine_client.py helpers (#5037)

Review: da39a3ee5e6b4b0d3255bfef95601890afd80709@wcourtney 
quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq