Micro-optimization: replace list lookup with set membership (#1046)

In `qsimcirq/qsim_circuit.py`, changing the list `GATE_PARAMS` to a set
will result in O(1) lookups. Not likely to make a big difference for the
small set size, but perhaps it might shave some time off when many
simulations are executed.

Author: mhucka

qsimcirq/qsim_circuit.py

@@ -19,8 +19,8 @@
 
 from . import qsim
 
-# List of parameter names that appear in valid Cirq protos.
-GATE_PARAMS = [
+# Set of parameter names that appear in valid Cirq protos.
+GATE_PARAMS = {
     "exponent",
     "phase_exponent",
     "global_shift",
@@ -29,7 +29,7 @@
     "axis_phase_exponent",
     "phi",
     "theta",
-]
+}
 
 
 def _translate_ControlledGate(gate: cirq.ControlledGate):