Switch 0FC to production feature bit

[tankyleo]

Fixes #4230

I cannot remember if we reached any conclusions at the spec meeting, so I push the PR in case we want to land this in the 0.3 release.

cc @TheBlueMatt @carlaKC

[ldk-reviews-bot]

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[ldk-claude-review-bot]

I've thoroughly reviewed every hunk in this diff. The feature bit migration from staging (141) to production (41) is mechanically correct:

• Feature bit 41 correctly maps to byte 5 (40/8 = 5), matching the placement in all three context arrays (InitContext, NodeContext, ChannelTypeContext).
• The empty-byte comma counts are correct: 11 commas for bytes 8-18 in Init/NodeContext, replacing the old 9 commas + staging entry + 1 comma.
• ChannelTypeContext correctly stops at byte 6 since there are no features beyond it after the move.
• All method names (supports_anchor_zero_fee_commitments, requires_anchor_zero_fee_commitments, etc.) are unchanged, so all call sites continue to work without modification.
• No stale AnchorZeroFeeCommitmentsStaging references remain in the codebase.
• Feature definition ordering is correct: OnionMessages (39), AnchorZeroFeeCommitments (41), ProvideStorage (43).

No issues found.

Note (not a bug): Channels opened with the old staging bit 141 (by users who enabled negotiate_anchor_zero_fee_commitments on pre-release builds) will fail to deserialize after this change — FundedChannel deserialization at channel.rs:16293 will return UnknownRequiredFeature since bit 141 becomes unknown. The CHANGELOG already documents this as expected ("feature signaling may change in a future version of LDK, breaking compatibility"), and the feature defaults to off, so this is a known/accepted trade-off rather than a bug.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.20%. Comparing base (688544d) to head (5ab28b1).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4515      +/-   ##
==========================================
+ Coverage   86.14%   86.20%   +0.06%     
==========================================
  Files         160      160              
  Lines      108046   108410     +364     
  Branches   108046   108410     +364     
==========================================
+ Hits        93080    93459     +379     
+ Misses      12346    12321      -25     
- Partials     2620     2630      +10     

Flag	Coverage Δ
tests	86.20% <100.00%> (+0.06%)	⬆️

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[TheBlueMatt]

I don't recall either. ACKing this but let's double check with t-bast IIRC the conclusion was "yea, probably just merge spec PR" so we should do this but we should check in at the spec meeting.

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