feat(backup): expose incremental_base_backup_id on BackupListReturn (#2069)

[Anai-Guo]

Closes #2069.

Problem

Weaviate's GET /backups/{backend} returns incremental_base_backup_id on every item — BackupListResponseItems0 declares it, and Scheduler.List populates it for callers the handler has confirmed as root.

BackupListReturn doesn't declare the field, so executor.list_backups() (BackupListReturn(**entry)) silently drops it. There is currently no way to tell from client.backup.list_backups(...) which base backup an incremental backup was built on — the only alternative is a get_create_status() round trip per backup.

Change

One field on BackupListReturn:

incremental_base_backup_id: Optional[str] = Field(default=None)

The JSON key is snake_case server-side (json:"incremental_base_backup_id,omitempty"), so it matches the field name and needs no alias. Optional[str] with default=None is deliberate rather than a required field: the server omits the key for non-incremental backups, and also for any caller it has not confirmed as root, so its absence must stay non-fatal.

Nothing else changes — no alias on an existing field is touched, and no other model is affected.

Verification

test/test_backup.py (new, no server or network needed):

• the field is surfaced when the server sends it, alongside the existing fields
• it defaults to None both when the key is omitted and when it is explicitly null

Run against the real package with only weaviate/backup/backup.py swapped:

before the change   3 failed   (AttributeError: 'BackupListReturn' object has no attribute 'incremental_base_backup_id')
after the change    3 passed

Also confirmed BackupListReturn(**entry) still parses an entry that has no incremental_base_backup_id key — the pre-existing behaviour is unchanged.

Lint, at the versions pinned in .pre-commit-config.yaml / main.yaml, over both changed files:

ruff 0.14.7 check             All checks passed!
ruff 0.14.7 format --diff     2 files already formatted
flake8 7.3.0 (+bugbear 24.12.12, comprehensions 3.17.0, builtins 3.0.0, docstrings 1.7.0, pydoclint 0.7.3)   clean

test/ is outside the pyright matrix (weaviate, integration, integration_embedded) and is covered by the unit-tests job.

Note

I left docs/changelog.rst alone since it only carries released versions and no Unreleased section — happy to add an entry under whichever version you're cutting if you'd prefer it in this PR.

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