[Feature] Introduce TestnetV0 Network Impl

[raychu86]

Motivation

This PR introduces a TestnetV0 network implementation alongside the existing MainnetV0.

A testnet version of AleoV0 and Circuit were also added to support the TestnetV0 network variant; they are AleoTestnetV0 and TestnetCircuit, respectively.

This new network variant will allow testnets to run with custom attributes. The current changes are:

• MAX_CERTIFICATES: 10 in MainnetV0 --> 100 in TestnetV0
• GENESIS_COINBASE_TARGET: (1023 in MainnetV0) --> 31 in TestnetV0
• GENESIS_PROOF_TARGET: (256 in MainnetV0) --> 8 in TestnetV0

The parameters crate was also updated to support and store the new testnet parameters.