Add LSPS5 DOS protections.

[martinsaposnic]

When handling an incoming LSPS5 request, the manager will check
if the counterparty is 'engaged' in some way before responding.
Engaged meaning = active channel | LSPS2 active operation | LSPS1 active operation.

Logic: If not engaged then reject request;

A single test is added only checking for the active channel condition,
because it's not super easy to get LSPS1-2 on the correct state to check this (yet).
Other tangential work is happening that will make this easier and more tests will come in the near future.

A few decisions that could be changed:

• the DOS protections are optional (default true). maybe this should not be configurable?
• I made the dos_protection_enforcer generic enough so it would be possible to add more behavior in the future. also some logic could be moved here like the ignored_peers logic from the manager, which could make sense to move to the dos enforcer

thoughts @tnull ?

[ldk-reviews-bot]

👋 Thanks for assigning @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[codecov]

Codecov Report

❌ Patch coverage is 60.41667% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.72%. Comparing base (dc335e9) to head (28d6286).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning-liquidity/src/lsps2/service.rs	0.00%	15 Missing ⚠️
lightning-liquidity/src/dos_protection_enforcer.rs	50.00%	3 Missing ⚠️
lightning-liquidity/src/manager.rs	94.73%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3993      +/-   ##
==========================================
- Coverage   88.97%   88.72%   -0.25%     
==========================================
  Files         174      174              
  Lines      124222   124467     +245     
  Branches   124222   124467     +245     
==========================================
- Hits       110522   110433      -89     
- Misses      11217    11615     +398     
+ Partials     2483     2419      -64     

Flag	Coverage Δ
fuzzing	?
tests	88.72% <60.41%> (-0.08%)	⬇️

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