Batch updates for 15.1.0

[wiboris]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

If an SDK is being regenerated based on a new API spec, a link to the pull request containing these API spec changes should be included above.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

This PR updates the azure-batch package for the 15.1.0 GA release by pointing generation at a newer azure-rest-api-specs commit and aligning the SDK surface with regenerated names/signatures.

Changes:

• Updated tsp-location.yaml to a newer azure-rest-api-specs commit.
• Renamed the Batch client “list subtasks” method shape (list_sub_tasks → list_subtasks) across sync/async code and tests.
• Refactored XML serialization/deserialization helpers in model_base.py, and updated docs/changelog for 15.1.0 GA.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
sdk/batch/azure-batch/tsp-location.yaml	Bumps the API spec commit used for TypeSpec generation.
sdk/batch/azure-batch/tests/test_batch.py	Updates tests to call list_subtasks.
sdk/batch/azure-batch/azure/batch/aio/_patch.py	Adjusts aio client patch typing/docstrings for async credentials.
sdk/batch/azure-batch/azure/batch/aio/_operations/_patch.py	Changes default max_concurrency to Optional[int] = None for aio bulk task creation helper.
sdk/batch/azure-batch/azure/batch/aio/_operations/_operations.py	Renames subtasks request builder/method usage to subtasks.
sdk/batch/azure-batch/azure/batch/_utils/model_base.py	Refactors XML (de)serialization namespace handling and element naming.
sdk/batch/azure-batch/azure/batch/_operations/_patch.py	Changes default max_concurrency to Optional[int] = None for sync bulk task creation helper.
sdk/batch/azure-batch/azure/batch/_operations/_operations.py	Renames subtasks request builder and public method to list_subtasks.
sdk/batch/azure-batch/apiview-properties.json	Updates APIView mapping for renamed list_subtasks methods.
sdk/batch/azure-batch/README.md	Updates enum reference in examples (currently to models._enums).
sdk/batch/azure-batch/CHANGELOG.md	Expands 15.1.0 GA notes with breaking-changes details.