Kinesis binding: Prevent stream ARN resolution in SharedThroughput mode (fix nil pointer error)

[swatimodi-scout]

Expected Behavior

When KinesisConsumerMode is set to SharedThroughput (default), the binding should not attempt to resolve the stream ARN. Stream ARN resolution should only occur in ExtendedFanout mode.

Actual Behavior

The code unconditionally invoked authProvider.Kinesis().Stream(...) and attempted to dereference the result.
When running in SharedThroughput mode, this led to a nil pointer error if the stream was unavailable or not initialized.

This was observed while running against LocalStack, but can occur in any environment where the stream cannot be resolved.

Steps to Reproduce the Problem

1. Configure the Kinesis input binding without explicitly setting KinesisConsumerMode (defaults to SharedThroughput).
2. Run the service.
3. Observe a crash with a nil pointer error from the unconditional Stream(...) call.

Release Note

FIX: Kinesis binding no longer resolves stream ARN when in 'SharedThroughput' mode, preventing nil pointer errors. ARN resolution is now limited to 'ExtendedFanout' mode only.

RELEASE NOTE: