* samples: Add Soft Delete policy and object management samples

Adds complete code samples demonstrating the following operations:
- storage_disable_soft_delete
- storage_get_soft_delete_policy
- storage_set_soft_delete_policy
- storage_list_soft_deleted_objects
- storage_list_soft_deleted_object_versions
- storage_restore_object

* remove conflict

* bug fix

* refactor: Use literal for retention duration and improve test assertion

- Removed the SOFT_DELETE_RETENTION_SECONDS constant, replacing it with
the literal value (604800) and adding a comment.
- Updated the listSoftDeletedObjectVersions test to assert on the object
generation number, improving test coverage and reflecting the logging
change.

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

chore(python): remove configure_previous_major_version_branches from python post processor

Source-Link: googleapis/synthtool@6702a34
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:bb3dc6c75c5f3e1a8928474f2dc8d9bbfa7b809045515764b9ff48c070cf2321

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

* feat(listBuckets): Add support for returning partial success

Implements the optional parameter `returnPartialSuccess`.

If set to `true` and the API response contains an `unreachable` array,
the function will return a successful callback (`err: null`) and pass
the `unreachable` array as the 5th argument.

This allows users to process the available buckets without the entire
operation failing on soft errors.

* docs(samples): Add listBucketsPartialSuccess sample

New sample for partial success in ListBuckets
(storage_list_buckets_partial_success)

* code refactor

* minor fix

* Ensure positional consistency for optional callback results

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* Enable partial success via placeholder objects

* bug fix

* addressing commends

* refactor: Simplify partial success placeholder logic

* addressing comments

* Revert "addressing comments"

This reverts commit 10a7e87.

* addressing comments

* chore: Clean up unreachable placeholder creation loop

* refactor: test case

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>