Add local network to network enum

[Oscar-Pepper]

Adds LocalNetwork variant to Network enum and adds methods for LocalNetwork for defining common network upgrade activation height patterns.

This allows production code of consumers to be tested in a regtest environment by easily switching out network parameters without needing to create their own version of the Network enum with a regtest variant.

[nuttycom]

NACK. This is not how the Network type is intended to be used; in circumstances where a local network is necessary, you should use a bespoke type that implements the Parameters trait. See how LocalNetwork is used in https://github.com/zcash/librustzcash/blob/main/zcash_client_sqlite/src/testing.rs for an example.

If there are places where we are depending upon the Network type that we shouldn't be, I'm happy to change those. There may be places where instead we should be taking a NetworkType parameter, rather than a Network (where we only need the network constants), otherwise everything should be a polymorphic type having the consensus::Parameters bound.

[Oscar-Pepper]

NACK. This is not how the Network type is intended to be used; in circumstances where a local network is necessary, you should use a bespoke type that implements the Parameters trait. See how LocalNetwork is used in https://github.com/zcash/librustzcash/blob/main/zcash_client_sqlite/src/testing.rs for an example.

If there are places where we are depending upon the Network type that we shouldn't be, I'm happy to change those. There may be places where instead we should be taking a NetworkType parameter, rather than a Network (where we only need the network constants), otherwise everything should be a polymorphic type having the consensus::Parameters bound.

Ok thanks for the info, our wallet struct contains an enum similar to NetworkType instead of a generic like WalletDb in testing.rs. It makes sense for us to eventually restructure this so we can be more aligned with librustzcash but for now I will just send the constructors for LocalNetwork so we can use it in place of our own LocalNetwork struct which is essentially the same.

[Oscar-Pepper]

closed for #1281