Implement shard communication channels for MPC circuits #3831

Job	Run time
Basic Checks	6m 50s
Additional Builds and Concurrency Tests	8m 23s
miri	4m 42s
Measure coverage	8m 45s
Release builds and tests	4m 11s
sanitize (address)	4m 19s
sanitize (address, multi-threading)	4m 11s
sanitize (leak)	3m 11s
sanitize (leak, multi-threading)	4m 47s
	49m 19s

Provide feedback