Fixing LoanBrokerCoverClawback to check for lsfMPTCanLock flag

[vlntb]

High Level Overview of Change

Add missing lsfMPTCanLock flag check to LoanBrokerCoverClawback transaction to comply with XLS-66 specification requirements.

Context of Change

• Added lsfMPTCanLock validation in LoanBrokerCoverClawback::preclaimHelper<MPTIssue>()
• Added unit test to verify both lsfMPTCanClawback and lsfMPTCanLock flags are required

Type of Change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Refactor (non-breaking change that only restructures code)
• [ ] Performance (increase or change in throughput and/or latency)
• [ ] Tests (you added tests for code that already exists, or your new feature included in this PR)
• [ ] Documentation update
• [ ] Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• [ ] Release

API Impact

• [ ] Public API: New feature (new methods and/or new fields)
• [ ] Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• [ ] libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• [ ] Peer protocol change (must be backward compatible or bump the peer protocol version)

[ximinez]

This PR essentially reverts commit 40cd57355db2f5367184a814367b3634505ab838, which I recently added due to comment: https://github.com/XRPLF/rippled/pull/5270#discussion_r2560543251

[vlntb]

This PR essentially reverts commit 40cd573, which I recently added due to comment: #5270 (comment)

Ok. If the consensus is that lsfMPTCanClawback can be set without lsfMPTCanLock. Then we can close this PR, as the system behaves as expected and concentrate on getting consistent results between local and network setups.