Serialize blinded Trampoline hops

[arik-so]

Add BlindedForward and BlindedReceive variants to OutboundTrampolinePayload.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.89%. Comparing base (66fb520) to head (9d01751). Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/msgs.rs	97.50%	0 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3007      +/-   ##
==========================================
+ Coverage   89.66%   90.89%   +1.23%     
==========================================
  Files         126      127       +1     
  Lines      102676   115370   +12694     
  Branches   102676   115370   +12694     
==========================================
+ Hits        92062   104864   +12802     
+ Misses       7894     7854      -40     
+ Partials     2720     2652      -68     

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[TheBlueMatt]

CI is quite sad.

[TheBlueMatt]

Feel free to squash before any reviewers take a big look.

[TheBlueMatt]

Looks like this needs rebase and CI was failing.