Adding a custom http client causes stall-stream protection to trigger if request takes too long

### Describe the bug

I added a custom http client like this:
https://github.com/BoundaryML/baml/pull/1827/files#top

but then my requests to bedrock stopped failing if they took longer than 5s with:
```
DispatchFailure(
DispatchFailure {
source: ConnectorError {
kind: Timeout,
source: ThroughputBelowMinimum {
expected: Throughput {
bytes_read: 1,
per_time_elapsed: 1s,
},
actual: Throughput {
bytes_read: 0,
per_time_elapsed: 1s,
},
},
connection: Unknown,
},
},
)
```

To fix it I had to disable streamstall protection:
https://github.com/BoundaryML/baml/pull/1877/files

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Expected Behavior

Don't fail with a timeout

### Current Behavior

Fails with an error

### Reproduction Steps

Add a custom http client like in: https://github.com/BoundaryML/baml/pull/1827/files#top

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### Version

```text
1.85.0
```

### Environment details (OS name and version, etc.)

macos

### Logs

_No response_

Start by comparing the custom HTTP client setup in PR #1827 with the stream-stall protection disabled in PR #1877, then trace how the SDK applies stall-stream timeouts to Bedrock responses. Reproduce with the issue's macOS setup and version 1.85.0; done means a request taking longer than 5 seconds no longer fails solely with ThroughputBelowMinimum while protection remains appropriate.

Written by the indexing model from the issue text.