Feature/msg builders

[bobozaur]

This PR introduces message builders through the typed-builder crate. The builder are based on the typestate pattern, but the crate is (at least advertised) to be fully compatible/replaceable by the derive-builder trait, which is using runtime construction of the type and allows for more flexibility (like passing builders around).

The typestate vs runtime construction decision will essentially depend on whether consumers want/need to build messages themselves and how convoluted these processes usually get. We don't really have to decide now, but it's a good thing to consider in the future.

For consistency reasons even some single fielded protocol specific messages contents implement builders, so that it is convenient, uniform and easy to know how one would go about composing a message.

There are some inner types which also implement the builders, yet for some types it is indeed quite the overkill (like CredentialPreview). I might revisit such types and just implement plain old new() constructors.

Another change that this PR brings is a uniformization of the Invitation message from the Connection protocol, so that the same decorators are used regardless of invitation type. The rationale is that it's much easier to reason with the invitation this way and since the protocol is old and won't be suffering changes it should be fine to simply deal with it like this.

Also, this addresses #949 .

[codecov-commenter]

Codecov Report

Merging #972 (66eaf07) into main (7558c3d) will decrease coverage by 0.54%.
The diff coverage is 42.74%.

@@            Coverage Diff             @@
##             main     #972      +/-   ##
==========================================
- Coverage   29.76%   29.23%   -0.54%     
==========================================
  Files         411      414       +3     
  Lines       26070    26246     +176     
  Branches     5315     5365      +50     
==========================================
- Hits         7760     7672      -88     
- Misses      16001    16263     +262     
- Partials     2309     2311       +2     

Flag	Coverage Δ
unittests-aries-vcx	29.23% <42.74%> (-0.54%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
...vcx/src/handlers/connection/mediated_connection.rs	0.00% <0.00%> (ø)
aries_vcx/src/handlers/discovery/mod.rs	0.00% <ø> (ø)
aries_vcx/src/handlers/issuance/holder.rs	42.13% <0.00%> (-0.54%)	⬇️
aries_vcx/src/handlers/out_of_band/receiver.rs	0.00% <0.00%> (ø)
...ries_vcx/src/handlers/proof_presentation/prover.rs	38.59% <0.00%> (+2.53%)	⬆️
...es_vcx/src/handlers/proof_presentation/verifier.rs	39.37% <0.00%> (+0.11%)	⬆️
aries_vcx/src/protocols/connection/generic/mod.rs	9.30% <0.00%> (-0.30%)	⬇️
aries_vcx/src/protocols/connection/mod.rs	4.54% <0.00%> (-0.07%)	⬇️
...ocols/issuance/issuer/states/requested_received.rs	37.50% <ø> (ø)
...ocols/mediated_connection/invitee/state_machine.rs	0.00% <0.00%> (ø)
... and 67 more

... and 5 files with indirect coverage changes

[Patrik-Stas]

This is great! Looks a lot cleaner, much easier to read. Very nice 👍

[mirgee]

Love it! Makes message construction a breeze - so much easier on the eyes, the programmer is easily guided by the code completion now and I like that it is guaranteed that all mandatory fields are set at compile time 👍

[gmulhearn]

Very epic! Cannot wait to use this