[v0.21.x-branch] Backport #11032: contractcourt: retain deadline across contest resolution

[github-actions]

Backport of #11032

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Change Description

Outgoing contest resolvers embed the timeout resolver they transition to once
the outgoing HTLC reaches its expiry. Forward the corresponding incoming HTLC
expiry to that embedded resolver so the existing deadline remains available
after the transition.

The added test exercises the contest-to-timeout transition and checks that the
supplied deadline is retained.

Steps to Test

go test ./contractcourt \
  -run 'TestHtlcOutgoingResolver(SupplementDeadline|Timeout|RemoteClaim) \
  -count=1

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the changed behavior are included.

Code Style and Documentation

• The change follows the code documentation and line-length guidelines.
• Commits follow the ideal Git commit structure.
• A change description is included in the 0.21.2 release notes.

[ziggie1984]

LGTM (no merge conflicts)