benchmark: Add ProxiedServer benchmark.
benchmark: Add ProxiedServer benchmark.

Here are the results of all single byte rpcs for comparison.
Benchmark____1B-12              	   50000	    377124 ns/op	   0.01 MB/s
Benchmark____1B_ClientTPCav-12  	   20000	    686344 ns/op	   0.00 MB/s
Benchmark____1B_ServerTPCav-12  	   20000	    726849 ns/op	   0.00 MB/s
Benchmark____1B_ProxiedServer-12	   30000	    492016 ns/op	   0.00 MB/s

Change-Id: I813eb6ee9a5ccb001767724ff89541332c307d33

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref