fix: z_validateaddress bug

[dorianvp]

Motivation

When receiving a regtest t-address in z_validateaddress it fails because it is parsing it as a testnet address, even when running on regtest. This mismatch makes the endpoint return an "invalid" response, when it should be valid.

Solution

If Zebra receives a t-address and the network is not mainnet, we treat regtest as equal to testnet.

Tests

Added rpc_z_validateaddress_regtest for testing this scenario.

Specifications & References

We're implementing this endpoint on Zaino here, and we encountered this issue there too.

The presence of this bug was previously discussed here.

Follow-up Work

PR Checklist

• The PR name is suitable for the release notes.
• The PR follows the contribution guidelines.
• The library crate changelogs are up to date.
• The solution is tested.
• The documentation is up to date.

[arya2]

Thank you!