Relay onion messages to compact node id

[thomash-acinq]

To save space, blinded routes may use a compact node id (scid + direction instead of public key) as an introduction node. When using such a compact route, the sender must use it's knowledge of the network to convert that to a public key, however trampoline users don't have that knowledge, they must transmit the compact route to the trempoline provider. We extend the spec to allow compact node ids in the next_node_id field.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.95%. Comparing base (e66e6d2) to head (3476289).
⚠️ Report is 330 commits behind head on master.

Files with missing lines	Patch %	Lines
...c/main/scala/fr/acinq/eclair/io/MessageRelay.scala	80.76%	5 Missing ⚠️
...src/main/scala/fr/acinq/eclair/EncodedNodeId.scala	66.66%	1 Missing ⚠️
.../scala/fr/acinq/eclair/message/OnionMessages.scala	66.66%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2821      +/-   ##
==========================================
+ Coverage   85.86%   85.95%   +0.08%     
==========================================
  Files         216      219       +3     
  Lines       18228    18429     +201     
  Branches      772      772              
==========================================
+ Hits        15652    15840     +188     
- Misses       2576     2589      +13     

Files with missing lines	Coverage Δ
...ir-core/src/main/scala/fr/acinq/eclair/Setup.scala	75.14% <100.00%> (ø)
...-core/src/main/scala/fr/acinq/eclair/io/Peer.scala	87.71% <100.00%> (ø)
...rc/main/scala/fr/acinq/eclair/io/Switchboard.scala	85.71% <100.00%> (ø)
...c/main/scala/fr/acinq/eclair/message/Postman.scala	93.33% <100.00%> (ø)
...cinq/eclair/payment/receive/MultiPartHandler.scala	93.33% <ø> (ø)
...a/fr/acinq/eclair/wire/protocol/MessageOnion.scala	92.50% <ø> (ø)
...la/fr/acinq/eclair/wire/protocol/OfferCodecs.scala	100.00% <100.00%> (ø)
...ala/fr/acinq/eclair/wire/protocol/OfferTypes.scala	96.36% <ø> (ø)
.../fr/acinq/eclair/wire/protocol/RouteBlinding.scala	97.72% <100.00%> (+0.05%)	⬆️
...src/main/scala/fr/acinq/eclair/EncodedNodeId.scala	66.66% <66.66%> (ø)
... and 2 more

... and 25 files with indirect coverage changes

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[t-bast]

Looks mostly good

[thomash-acinq]

Merged #2826 and added some TODO to correctly forward messages to ourself.

[t-bast]

LGTM