Bump SSZ version for larger bitfield SmallVec

[paulhauner]

Issue Addressed

NA

Proposed Changes

Bumps the ethereum_ssz version, along with other crates that share the dep.

Primarily, this give us bitfields which can store 128 bytes on the stack before allocating, rather than 32 bytes (sigp/ethereum_ssz#38). The validator count has increase massively since we set it at 32 bytes, so aggregation bitfields (et al) now require a heap allocation. This new value of 128 should get us to ~2m active validators.

Additional Info

• Bitfields have been moved from ssz_types to ethereum_ssz, so there's some non-substantial changes to error handling.
• The MetaData struct in lighthouse_network holds two bitfields and therefore now has a larger stack size. I had to Arc it to avoid some clippy lints about disparate enum sizes.
• An Attestation is now 96 bytes larger than it was before (32-128). You'll see some tests updated to expect these new sizes.

[michaelsproul]

We have a node running this branch on infra, are you planning to post some charts with metrics once it's been running for a little while?

I guess we're looking for lower total allocations per second, and maybe (indirectly) lower memory usage due to fragmentation. I don't imagine we get a noticeable reduction in CPU usage?