feat: Add specific error type for -rpcuser and -rpcpassword usage

[oleonardolima]

Description

As discussed in #68 trying to use the -rpcuser and -rpcpassword leads to an infinite loop, because this authentication method does not work alongside cookie authentication leading to an empty file, and the BitcoinD keeps retrying indefinitely.

This PR adds:

• a new Error variant for this RpcUserAndPasswordUse
• a new function to validate the args specified
• two new tests, one for -rpcuser and -rpcpassword usage, which asserts a failure, and another one for the usage of -rpcauth which works fine alongside cookie authentication.

Fixes #68

[RCasatta]

Concept ACK.

I would prefer not to add the "regex" crate if not strictly necessary, in this case, I think fn starts_with could do the job without an additional dependency?

Without regex this PR is an improvement and already mergeable to me.

A further improvement is to make args field a new type Args struct with a couple of functions to add an arg (at this point check arg validity) and to returns the args. This struct should consider also #39

[oleonardolima]

Concept ACK.

I would prefer not to add the "regex" crate if not strictly necessary, in this case, I think fn starts_with could do the job without an additional dependency?

Without regex this PR is an improvement and already mergeable to me.

A further improvement is to make args field a new type Args struct with a couple of functions to add an arg (at this point check arg validity) and to returns the args. This struct should consider also #39

@RCasatta Thanks for the review and the suggestion

Yep, it does not really need the regex to do it, I updated it to have an invalid argument list and check from that list using the starts_with instead.

[RCasatta]

utACK 54e444a

Ideally when commits in the same PR touch the same lines touched by other commits in the same PR is better to squash, next time :)

[oleonardolima]

utACK 54e444a

Ideally when commits in the same PR touch the same lines touched by other commits in the same PR is better to squash, next time :)

Thanks, I forgot to squash it, sorry 😁

I'll try to take a look at the other improvement to use Args