perf(pp): skip serialization and digest of commitment key

[chaosma]

Issue Link / Motivation

Close #136

Changes Overview skip serialization of commitment keys.

With table size k=17 and commitment key of size 2^27, i.e. each key has 8GB size.

time profile before

··Start:  pp_new
····Start:  primary
······Start:  circuit_collect_plonk_struct
······End:    circuit_collect_plonk_struct.................................0.38s
····End:    primary........................................................0.38s
····Start:  secondary
······Start:  process_step
······End:    process_step.................................................0.00s
······Start:  circuit_collect_plonk_struct
······End:    circuit_collect_plonk_struct.................................0.24s
······Start:  circuit_collect_witness
······End:    circuit_collect_witness......................................0.10s
······Start:  generate_plonk_trace
······End:    generate_plonk_trace.........................................0.07s
····End:    secondary......................................................0.43s
····Start:  digest
······Start:  digest_to_bits
······End:    digest_to_bits..............................................59.00s
····End:    digest........................................................59.00s
··End:    pp_new..........................................................59.80s

after

··Start:  pp_new
····Start:  primary
······Start:  circuit_collect_plonk_struct
········Start:  compressed_gates
········End:    compressed_gates...........................................0.00s
······End:    circuit_collect_plonk_struct.................................0.37s
····End:    primary........................................................0.37s
····Start:  secondary
······Start:  process_step
······End:    process_step.................................................0.00s
······Start:  circuit_collect_plonk_struct
······End:    circuit_collect_plonk_struct.................................0.24s
······Start:  circuit_collect_witness
······End:    circuit_collect_witness......................................0.10s
······Start:  generate_plonk_trace
······End:    generate_plonk_trace.........................................0.08s
····End:    secondary......................................................0.43s
····Start:  digest
······Start:  digest_to_bits
······End:    digest_to_bits...............................................1.69s
····End:    digest.........................................................1.69s
··End:    pp_new...........................................................2.49s

memory profile

Before:

dhat: Total:     46,145,901,258 bytes in 7,481,137 blocks
dhat: At t-gmax: 26,414,849,327 bytes in 15,103 blocks
dhat: At t-end:  503,405 bytes in 810 blocks

After

dhat: Total:     37,553,398,397 bytes in 7,441,377 blocks
dhat: At t-gmax: 18,205,173,065 bytes in 29,544 blocks
dhat: At t-end:  503,405 bytes in 810 blocks