[dougchansan]

PR #12 adds bounded hashing for large save files, but its single-file writer reports failure after successfully replacing saveg.dat: postwrite verification checks the replacement against both the new payload and the original backup.

This PR carries forward the original contributor commit from #12 and adds a fix:

• Verify the target against the replacement payload, including its displayed status.
• Compare only preserved files against the original backup.
• Retain the prewrite backup comparison and missing-target/read-back failure checks.
• Add seven offline tests that execute the actual writer with in-memory engine adapters.

Validation:

• All seven writer regression tests and three existing hash-helper tests pass locally.
• The changed-replacement test fails against the original Allow Elden Ring saves and verify large writes in chunks #12 source with "Preserved file differs after commit" and passes with this fix.
• Syntax and whitespace checks pass.
• No hardware execution was performed for this fix.

The GitHub integration could not update the contributor's branch ("Resource not accessible by integration"), so the corrected changes are published here. The original contributor commit and authorship are preserved. This is the corrected replacement for #12.