Use valuable::Enumerable to iterate through network upgrades

[teor2345]

Is your feature request related to a problem? Please describe.

Some of Zebra's tests iterate through the entire set of network upgrades. Others want to know the latest network upgrade, even if it doesn't have an activation height.

If we use the valuable crate's Enumerable derive, we won't need to change these tests every time we add a new network upgrade.

https://github.com/tokio-rs/valuable

Describe the solution you'd like

• Wait for valuable to be published to https://crates.io/crates/valuable
  • possibly outdated plans: https://tokio.rs/blog/2021-05-valuable
• Derive Enumerable for NetworkUpgrade

A list of network upgrades:

• Change the version_consistent test to use Enumerable's EnumDef
• Check if any zebra_chain::parameters tests could also use EnumDef

The latest network upgrade (even if it doesn't have an activation height):

• Use EnumDef to find future network upgrades in Arbitrary for LedgerState
  • and Default for LedgerState and LedgerStateOverride if we haven't removed them in Increase proptest coverage using arbitrary LedgerStates #2059
• Replace hard-coded instances of Canopy, NU5, and future network upgrades with a "latest network upgrade" function, as needed
  • Replace the NU5 constant in zebra-chain/src/transaction/tests/vectors.rs with the latest network upgrade
  • Replace the list of network upgrades in the Transaction::branch_id() strategy with EnumDef, a "has branch id" filter, then a random choice

Describe alternatives you've considered

We could use strum, but we're going to have the valuable dependency when tracing hits 1.0 anyway
https://docs.rs/strum/0.20.0/strum/

We could do nothing.

[dconnolly]

ooo this is handy

[teor2345]

This is not needed, the current code works.