Pytest: test to reproduce issue #9389 - #9390

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Changelog-None

Reproduce #9389

What this does

Adds test_closing_anysegwit_lost_unilateral to tests/test_closing.py, which reproduces the reported deadlock: a channel stuck in CHANNELD_SHUTTING_DOWN that cannot be closed cooperatively or unilaterally.

The test drives the exact sequence:

1. l1 and l2 open a channel while both offer option_shutdown_anysegwit, so l1 records a P2TR shutdown_scriptpubkey[LOCAL].
2. l2 goes away; l1 issues close with unilateraltimeout=0, which commits that script and moves the channel to CHANNELD_SHUTTING_DOWN.
3. l2 comes back with dev-force-features=-27, i.e. without option_shutdown_anysegwit.
4. l1 can no longer close the channel by any means.

Both RPC paths from the issue fail, and the channel stays stuck:

close <id> 1                       -> "Peer does not allow v1+ shutdown addresses"
close <id> 1 <bc1q...>       -> "... does not match already-sent shutdown script ..."