Introduce check for dangling RAA blockers in test_utils

[shaavan]

Partially addresses #3381

Summary

This PR addresses the issue of unhandled dangling RAA blockers during testing by introducing a check in Node::Drop().

Changes:

1. Added a validation in Node::Drop() to ensure no dangling RAA blockers remain unhandled.
2. Updated the test to handle RAA blockers, fixing the failure caused by the new validation.

[shaavan]

Updated from pr3504.01 to pr3504.02 (diff):
Addressed @jkczyz comments

Changes:

1. Updated get_and_clear_raa_blockers to pub(crate) to eliminate redundant test-specific declarations for other structs.

[codecov]

Codecov Report

Attention: Patch coverage is 92.10526% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.34%. Comparing base (85d1e5f) to head (1d95abe).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/chanmon_update_fail_tests.rs	90.00%	2 Missing ⚠️
lightning/src/ln/functional_test_utils.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3504      +/-   ##
==========================================
+ Coverage   88.32%   88.34%   +0.01%     
==========================================
  Files         149      149              
  Lines      112912   113080     +168     
  Branches   112912   113080     +168     
==========================================
+ Hits        99731    99898     +167     
- Misses      10694    10696       +2     
+ Partials     2487     2486       -1     

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