Core: Don't override equals() and hashCode() in V4 DeletionVector

[gaborkaszab]

The convention for V4 metadata structs like DeletionVectorStruct is that we don't override equals() and hashCode only if it's inevitable. See this comment on a previous PR. These overrides were meant to be removed/not added in that PR, however, somehow went under the radar and made it in.
This PR removes unintentionally adding the overrides.

[gaborkaszab]

cc @anoopj@stevenzwu@rdblue

[anoopj]

The change looks good to me. We don't rely on this currently so let's remove it.

[kevinjqliu]

im curious, what is the reasoning to remove these? It seems useful. Would it be a surprise later on when comparing DeletionVector?

I see it was added originally in 7c13104#diff-44ec3b66acad90f4f873b3786f55feb62bb03287626b41bd4622c11d5ca9963fR132-R150

[uros-b]

No comment documents the intended equality contract after this change. Equality is now identity-based, and the safety of that choice rests on the invariant that no caller puts DeletionVectorStruct in a Set/Map key or calls .equals() for value comparison. As key_metadata (#17438) and further V4 fields land, a future reader writing dedup/caching code could reasonably assume value equality is in place. A single class-level sentence; e.g. "Equality and hash code are identity-based; DeletionVectorStruct is a projection-backed view, not a value type" would protect this invariant. This is the same documentation gap present in none of the sibling structs (TrackedFileStruct etc.), so adding it here sets a useful precedent for the whole V4 family.

[uros-b]

@gaborkaszab Please note that the PR body is currently empty: no description, no linked issue, no rationale. Iceberg convention expects a description explaining why the override is being removed.

[nssalian]

@gaborkaszab the Rationale for this change isn't clear. Please add more details and context since reviewers here might not be aware. Happy to take a look once the reasoning is fleshed out.

[gaborkaszab]

Thanks for looking, @anoopj , @kevinjqliu , @uros-b , @nssalian !
The reason removing them is that they shouldn't have been added. The agreement is that we don't override them for V4 metadata structs. I added a PR description with more explanation and a link to a previous comment.

[kevinjqliu]

thanks for the context! ❤️

[amogh-jahagirdar]

Yeah thanks for cleaning this up @gaborkaszab! I will go ahead and merge