fix: preserve projected files across rebased writes

[lance-gatefixer]

Summary

• apply a rebased Delete by updating only the deletion file on the current fragment, including when Project may alter nullability
• prune fully projected-out files from updated and newly written fragments in every Update mode
• preserve files that still contain any live field and keep the field-id watermark correct

Root cause

Delete and Update manifest application reused fragment post-images staged against the transaction read version. When a concurrent Project pruned files whose fields were all removed, those stale post-images could restore the files during rebase. RewriteColumns could also restore a newly written file for a column the Project had removed.

Delete now carries only its deletion-file delta onto the current fragment. The same rule covers a Project with preserves_nullability set to false; both Update rewrite modes are rejected earlier by the nullability conflict pre-check. Update filters both updated and new fragment files against the live projected schema while retaining mixed files that still contain a live field.

Validation

• cargo fmt --all
• cargo test -p lance-table
• cargo clippy --all --tests --benches -- -D warnings

Fixes #9217

[lance-gatekeeper]

✅ Gate recommendation: approve.

With #9218 now in the base, this revision cleanly supplies the remaining Update half: it applies Project’s live-field rule to both staged updated fragments and new fragments, preserving mixed files while preventing fully projected-out files from returning. The strengthened Delete regression confirms the two fixes compose.