.Net: Optimize Redis GetBatchAsync for Performance Improvement

[atiq-bs23]

Motivation and Context

Current implementation makes sequential Redis calls for each key, leading to network latency and slower batch retrieval.

Description

The new implementation improves performance by batching Redis commands and executing them concurrently. This reduces network round-trips and speeds up the retrieval process.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests and integration tests pass, current tests are okay for this change.
• I didn't break anyone 😄