tests: test unilateral closing with unknown fees + cpfp with withdraw

[enaples]

Important

26.04 FREEZE March 11th: Non-bugfix PRs not ready by this date will wait for 26.06.

RC1 is scheduled on March 23rd

The final release is scheduled for April 15th.

Checklist

Before submitting the PR, ensure the following tasks are completed. If an item is not applicable to your PR, please mark it as checked:

• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.
• Important All PRs must consider how to reverse any persistent changes for tools/lightning-downgrade

Additional Info

The test is meant to test the ability to perform a Child Pays For Parent on an unilateral channel close with custom feerate.

Steps

1. Fund two nodes, only one with the ability to compute fees
2. Verify that one is not able to compute fees.
3. The node that is able to compute fees open a channel to the other
4. Send some sats while mine some block
5. The node which opened the channel is shut down
6. The other node (unable to compute fees) unilateral close the channel by manually setting the feerate
7. Verify that the closing transaction is stuck on mempool because ferate is too low
8. Perform a withdraw manually specifying fees
9. Verify a new onchain output on wallet
10. Startup the other node and verify that the channel state is updated

Changelog-None

[cdecker]

Rebased on top of master to see if it passes.

[cdecker]

The linter is not happy about the coding standards, @enaples please address the warnings and push again.