Cosmos: Cutover transactional batch operation to Driver

[simorenoh]

Migrates ContainerClient::execute_transactional_batch() from the legacy CosmosRequest + BatchOptions::apply_headers() + container_connection.send() pipeline to CosmosOperation + driver.execute_operation(), matching the pattern established in #4147, #4174, and #4128.

This was the last item-level operation using the old SDK pipeline for header manipulation, so the batch-specific helpers are removed as dead code.

Changes

azure_data_cosmos_driver/src/models/cosmos_operation.rs

• Added CosmosOperation::batch() factory (POST to items feed with partition
  key, OperationType::Batch), following the create_item pattern.

azure_data_cosmos/src/clients/container_client.rs

• Rewrote execute_transactional_batch to build a CosmosOperation::batch,
  apply options, execute through the driver, and bridge the response.
• Added apply_batch_options helper that takes &BatchOptions and wires
  session token onto the operation.
• Removed the items_link field from ContainerClient — it was only used by
  the batch method's old CosmosRequest path.

azure_data_cosmos/src/options/mod.rs

• Removed BatchOptions::apply_headers().
• Removed the apply_content_response_on_write_header() helper (sole caller
  was BatchOptions::apply_headers).
• Removed 4 batch header tests that validated the removed methods.
• Cleaned up unused imports.

azure_data_cosmos/src/constants.rs

• Removed the PREFER_MINIMAL constant, which is no longer referenced in the
  SDK crate. The driver handles this header internally via its operation pipeline.

[simorenoh]

/azp run rust - cosmos - weekly

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

This PR migrates ContainerClient::execute_transactional_batch() to the Cosmos Driver CosmosOperation execution path, aligning transactional batch with other item/query operations that have already been cut over and removing now-dead legacy header shims.

Changes:

• Add CosmosOperation::batch() factory for transactional batch requests.
• Route execute_transactional_batch() through driver.execute_operation() and bridge the driver response back to SDK types.
• Remove legacy SDK batch header helpers/tests and delete now-unused SDK constants/fields.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
sdk/cosmos/azure_data_cosmos_driver/src/models/cosmos_operation.rs	Adds a driver-level batch() operation factory targeting the items feed with a partition key.
sdk/cosmos/azure_data_cosmos_driver/src/models/cosmos_headers.rs	Introduces request header name constants needed for driver batch request construction.
sdk/cosmos/azure_data_cosmos_driver/src/driver/pipeline/operation_pipeline.rs	Emits required batch headers when OperationType::Batch and adds unit tests asserting header behavior.
sdk/cosmos/azure_data_cosmos/src/options/mod.rs	Removes legacy BatchOptions::apply_headers() and related helpers/tests now that batch is driver-routed.
sdk/cosmos/azure_data_cosmos/src/constants.rs	Removes PREFER_MINIMAL constant (no longer used by the SDK crate after cutover).
sdk/cosmos/azure_data_cosmos/src/clients/container_client.rs	Rewrites execute_transactional_batch() to build/execute a driver operation; removes items_link field and adds apply_batch_options.

[simorenoh]

/azp run rust - cosmos - weekly

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[analogrelay]

Love how straightforward these cutovers have become.