perf(continuations): Do not propagate touched addresses set to 0

[hratoanina]

Right now, we propagate to MemAfter all touched memory adresses (except pruned contexts). However, since uninitialized addresses are set to 0 by default (except for preinitialized segments), we can omit 0-value addresses from MemAfter. This would probably require one or two Memory columns, but would remove many rows from MemAfter and MemBefore.

[Nashtare]

We're actually at 28 columns already for Memory (I had forgotten the several ones added from context pruning), so we can afford to add 2. Given that we can actually allow up to 4 new columns before the next permutation, we may as well consider pre-initializing additional segments (if need be).

[hratoanina]

It's actually trickier than expected. On the branch https://github.com/0xPolygonZero/zk_evm/commits/no_zero_value_propagation/ there's a partial version which uses 32 columns total, and removes zero values only if context and segment are non-zero, which means that it's missing non-preinitialized segments in context 0. Including them would either require to go over 32 columns or come up with some clever constraints I haven't found yet. If the gains are enough as is I don't think we should bother.

[Nashtare]

As discussed on slack, it seems an approach on a segment basis may be more beneficial, according to initial benchmarks, as most of the overhead (outside of the Code and TrieData segments which can't be ignored) is coming from 3 segments including RlpRaw, whose filtering even in context 0 would bring benefits.