Aggregate BlindedPayInfo for blinded routes

[valentinewallace]

BOLT 12 invoices encode BlindedPayInfo(s) as part of their hints for routing, whose fields are computed by aggregating fee/cltv/etc values from the hops along the blinded path. Helps address #1970.

Based on #2412.

[codecov-commenter]

Codecov Report

Patch coverage: 88.19% and no project coverage change.

Comparison is base (61d896d) 90.59% compared to head (88a0063) 90.59%.
Report is 41 commits behind head on main.

❗ Current head 88a0063 differs from pull request most recent head 134f6f3. Consider uploading reports for the commit 134f6f3 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2514    +/-   ##
========================================
  Coverage   90.59%   90.59%            
========================================
  Files         110      110            
  Lines       57410    58062   +652     
  Branches    57410    58062   +652     
========================================
+ Hits        52008    52602   +594     
- Misses       5402     5460    +58     

Files Changed	Coverage Δ
lightning/src/blinded_path/mod.rs	100.00% <ø> (ø)
lightning/src/blinded_path/payment.rs	78.90% <85.59%> (+78.90%)	⬆️
lightning/src/ln/monitor_tests.rs	98.06% <85.71%> (-0.46%)	⬇️
lightning/src/chain/chainmonitor.rs	94.91% <97.22%> (-0.12%)	⬇️

... and 31 files with indirect coverage changes

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[valentinewallace]

Rebased to fix CI. I added test coverage for the min htlc computation to #2413 so this should be good for review.

[alecchendev]

Sorta confused by htlc_minimum_msat, everything else looks good

[TheBlueMatt]

Okay, sorry for all the noise here, only one comment left I think.

[valentinewallace]

I think I addressed all feedback. Thought I saw something about not decrementing htlc_min but I don't see it anymore?

[TheBlueMatt]

#2514 (comment) :)