## What happened

A LiteLLM managed Bedrock batch can be created and reach `InProgress`, but `POST /v1/batches/{managed_id}/cancel` fails before reaching AWS:

```text LiteLLM doesn't support bedrock for `cancel_batch`. Only openai, azure, and vertex_ai are supported. ```

The equivalent provider operation is AWS Bedrock `StopModelInvocationJob`.

## Reproduction

1. Configure a managed Bedrock batch model with `model_info.mode: batch`, an S3 staging bucket, and `aws_batch_role_arn`. 2. `POST /v1/files` with a valid 100-record JSONL file. 3. `POST /v1/batches` using the managed input file and wait for the provider job to reach `InProgress`. 4. `POST /v1/batches/{managed_batch_id}/cancel`.

Expected: LiteLLM calls `StopModelInvocationJob` and returns an OpenAI-compatible batch resource with `status=cancelling`, then `cancelled` when Bedrock reports `Stopped`.

Actual: LiteLLM returns HTTP 400 without calling Bedrock.

## Root cause

`litellm.cancel_batch` / `acancel_batch` only dispatches OpenAI, Azure, and Vertex batch cancellation. Bedrock has a retrieve handler for `GetModelInvocationJob`, but no corresponding cancellation handler for `StopModelInvocationJob`.

## Proposed behavi…