Handle chain information in explicit form in invoices

[dr-orlovsky]

This is a breaking change since inside the invoice structure we make chain non-optional; plus we add new error cases and make set_chain return Result. Thus I am making this PR against v11 branch.

Closes #103

[cryptoquick]

ACK
Very comprehensive tests cases. Looks good.
I also agree, 0.11 is a good place to put this.

[fedsten]

Any reason why it is non-optional instead of optional as discussed in #103?

[dr-orlovsky]

@fedsten the parameter is optional as was discussed, thus the invoice string is backwards-compatible. However, for each given invoice we always know which network it belongs to (since we are defaulting to mainnet as discussed), thus we must have a non-optional field in the rust API.

[fedsten]

Got it, for clarifying.

[dr-orlovsky]

In other words, a wallet will always know and be sure to which network a given invoice belongs. If the invoice has conflicting network information (like an address network doesn't match the network provided in a parameter) it will error during the parse procedure. But each parsed invoice always knows which network it is valid for, and is guaranteed not to have network conflicts between address and parameter.

[zoedberg]

I'm trying to review the PR but executing tests I'm encountering some issues.
It seems that the LoadError is defined only when the fs feature is active but then used in other parts of code available without that feature. Moreover, if I run tests activating all features, I receive the following error:

error[E0599]: no method named `assume_checked` found for struct `bp::Address` in the current scope
   --> invoice/src/parse.rs:454:14
    |
452 |           let addr_bc = Address::from_str("bc1qpws79r3ea4yy2ujsahwrmy2gutdj8w5whnhket")
    |  _______________________-
453 | |             .unwrap()
454 | |             .assume_checked();
    | |             -^^^^^^^^^^^^^^ method not found in `Address`
    | |_____________|
    | 

error[E0599]: no method named `assume_checked` found for struct `bp::Address` in the current scope
   --> invoice/src/parse.rs:457:14
    |
455 |           let addr_tc = Address::from_str("mxVFsFW5N4mu1HPkxPttorvocvzeZ7KZyk")
    |  _______________________-
456 | |             .unwrap()
457 | |             .assume_checked();
    | |             -^^^^^^^^^^^^^^ method not found in `Address`
    | |_____________|
    | 

For more information about this error, try `rustc --explain E0599`.
error: could not compile `rgb-invoice` (lib test) due to 2 previous errors

[dr-orlovsky]

@zoedberg wait, we do not have CI set up for this repo? Oh, I'll fix it.

I did this PR initially against v0.10 branch which is using rust-bitcoin v0.30. Then I understood it was breaking, so I moved to v0.11, which doesn't depend on rust-bitcoin at all and has a different Address type (from bp-std) with a different API. Thus the issue. Will fix.

[dr-orlovsky]

Closing in favor of solution from #118