Add unannounced_channel_max_inbound_htlc_value_in_flight_percentage

[tankyleo]

    Add `unannounced_channel_max_inbound_htlc_value_in_flight_percentage`

    Users can now configure two different max percentages for the channel
    value that can be allocated to inbound HTLCs, one for announced
    channels, and another for unannounced channels.

[ldk-reviews-bot]

👋 Thanks for assigning @TheBlueMatt 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.

[ldk-claude-review-bot]

Review Summary

No new issues found. All three issues from the previous review have been addressed:

1. Deserialization backwards-compatibility regression — Fixed. Both read and write paths now use get_legacy_default_holder_max_htlc_value_in_flight_msat() which hardcodes MAX_IN_FLIGHT_PERCENT_LEGACY.

2. Missing unit test for announced channel path — Fixed. test_configured_holder_max_htlc_value_in_flight now calls do_test_configured_holder_max_htlc_value_in_flight(true) and do_test_configured_holder_max_htlc_value_in_flight(false).

3. Doc nit — Was retracted; the doc correctly says "Default value: 10".

Cross-cutting Note

The default in-flight percentage for unannounced channels changes from 10% to 25%. Since announce_for_forwarding defaults to false, and create_unannounced_chan_between_nodes_with_value() doesn't pin the in-flight percentage, many existing tests (~30+ across offers_tests.rs, priv_short_conf_tests.rs, interception_tests.rs, onion_route_tests.rs) will silently see their unannounced channel in-flight limits increase from 10% to 25%. This appears intentional and is unlikely to cause test failures, but the often_offline_node_cfg() function in async_payments_tests.rs demonstrates good practice by explicitly pinning the old default for tests that depend on specific capacity behavior.

[codecov]

Codecov Report

❌ Patch coverage is 93.15068% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.01%. Comparing base (450c03a) to head (3644da0).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/util/config.rs	66.66%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4529      +/-   ##
==========================================
- Coverage   87.10%   87.01%   -0.10%     
==========================================
  Files         163      163              
  Lines      108740   108792      +52     
  Branches   108740   108792      +52     
==========================================
- Hits        94723    94669      -54     
- Misses      11531    11626      +95     
- Partials     2486     2497      +11     

Flag	Coverage Δ
fuzzing	39.37% <60.00%> (-0.83%)	⬇️
tests	86.20% <95.65%> (-0.01%)	⬇️

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