fix: use exn.rp field as recipient for exchange message (#3)

[lenkan]

All exchange messages now have the intended recipient in the payload, so the extra body parameter is confusing and could cause issues.

This PR removes the "rec" body parameter that previously specified a list of recipients of an exn message. This list had no correlation with the rp field in the exchange message payload.

This PR also removes the ipex multisig handlers, for no other reason that they weren't used in any of the signify integration tests, so to me it was unnecessary complexity. I do not see any reason to keep this feature as we already use the "/multisig/exn" from the client.

See discussions:

• Fix/test del rot multisig more signify-ts#267 (comment)
• Update POST /identifiers/name/exchanges endpoint to report recp field in POST body #270
• Bug: Exchanges.send() should not return early and instead execute for each recipient signify-ts#310
• fix: send exn for each recipient; no early return signify-ts#311

[codecov]

Codecov Report

❌ Patch coverage is 86.76471% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.10%. Comparing base (f621ca4) to head (09c556a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/keria/app/agenting.py	75.00%	8 Missing ⚠️
src/keria/peer/exchanging.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #396      +/-   ##
==========================================
- Coverage   87.76%   86.10%   -1.66%     
==========================================
  Files          26       26              
  Lines        5826     5650     -176     
==========================================
- Hits         5113     4865     -248     
- Misses        713      785      +72     

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[kentbull]

@lenkan will you rebase this on main? Also, is it ready for review?

[lenkan]

@kentbull Rebased on current main and ready for review. We have been running this code for about 6 months now.

One note on the controversial removal of the multisig IPEX route handlers: no Signify code paths used them at the time. I did not want two different ways of achieving the same thing. The /multisig/exn endpoint provides the same capability, and that is what the Signify integration tests use.

[iFergal]

Probably worth a refactor now or later to

if ked["r"] !== "/ipex/admit":
    raise falcon.HTTPBadRequest(
        description=f"invalid message route {route}"
    )

op = IpexAdmitCollectionEnd.sendAdmit(agent, hab, ked, sigs)

[iFergal]

But really, I have been thinking that an even bigger refactor that would be nice is to drop all IPEX endpoints in favour of just /identifiers/{name}/exchanges, and be able to register Decks based on the route, so agent.grants.append(dict(said=ked["d"], pre=hab.pre)) could be called dynamically.

[kentbull]

@lenkan please fix conflicts.