Fix reads for blocks freed after being cloned

[amotin]

PR #18421 fixed a case when reads for blocks cloned after being freed could return zeroes. But it created an opposite problem, when reads for blocks freed after being cloned could return non- zero content from the cloning.

This patch should fix the problem by creating a more specialized form of dnode_block_freed(), taking into account the TXG when the cloning has happened and checking frees only in TXGs after.

Fixes: #18421

How Has This Been Tested?

Not really.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[nbdd0121]

Do you have a test program so that I can run some red/green testing?

[amotin]

Do you have a test program so that I can run some red/green testing?

No, I don't. I wonder if you could invert your test or make it bidirectional.