Implement atomicity group handling and separate transactions for batch requests

[kbarbounakis]

Is your feature request related to a problem? Please describe.
Currently, batch requests in OData v4 leverage atomicity groups (changesets) to ensure groups of operations are processed within the same transaction. The current implementation lacks fine-grained support for executing each atomicity group (set of operations) as a distinct transaction within batch requests.

Describe the solution you'd like

• Implement logic to detect and group changesets/atomicity groups in batch requests according to OData v4 standards.
• Ensure each atomicity group is executed in a separate transaction, such that the success or failure of one group does not affect others.
• Roll back changes only within the failed atomicity group, while successfully committed groups remain intact (as per OData batch protocol).
• Handle correct response structure indicating the transaction status of each atomicity group.

Describe alternatives you've considered

• Treating the whole batch as a single transaction (already being handled in parent issue).

Additional context

• This sub-issue focuses only on atomicity/changset grouping and their transaction boundaries, not general batch transaction support.
• See OData v4 Batch Protocol: https://docs.oasis-open.org/odata/odata/v4.0/os/part1-protocol/odata-v4.0-os-part1-protocol.html#_Batch_Requests
• Parent issue: Implement transaction support for batch requests with POST operations #88