[SPARK-53371] Upgrade gRPC Swift NIO Transport to 2.1.0

### What changes were proposed in this pull request?

This PR aims to upgrade `gRPC Swift NIO Transport` to 2.1.0.

### Why are the changes needed?

To bring the latest improvements.
- https://github.com/grpc/grpc-swift-nio-transport/releases/tag/2.1.0
  - grpc/grpc-swift-nio-transport#122
  - grpc/grpc-swift-nio-transport#120
  - grpc/grpc-swift-nio-transport#115

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #218 from dongjoon-hyun/SPARK-53371.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Package.swift

@@ -36,7 +36,7 @@ let package = Package(
   dependencies: [
     .package(url: "https://github.com/grpc/grpc-swift-2.git", exact: "2.0.0"),
     .package(url: "https://github.com/grpc/grpc-swift-protobuf.git", exact: "2.0.0"),
-    .package(url: "https://github.com/grpc/grpc-swift-nio-transport.git", exact: "2.0.0"),
+    .package(url: "https://github.com/grpc/grpc-swift-nio-transport.git", exact: "2.1.0"),
     .package(url: "https://github.com/google/flatbuffers.git", branch: "v25.2.10"),
   ],
   targets: [

README.md

@@ -20,7 +20,7 @@ So far, this library project is tracking the upstream changes of [Apache Arrow](
 - [Swift 6.0 (2024) or 6.1 (2025)](https://swift.org)
 - [gRPC Swift 2 (May 2025)](https://github.com/grpc/grpc-swift-2/releases/tag/2.0.0)
 - [gRPC Swift Protobuf 2.0 (May 2025)](https://github.com/grpc/grpc-swift-protobuf/releases/tag/2.0.0)
-- [gRPC Swift NIO Transport 2.0 (May 2025)](https://github.com/grpc/grpc-swift-nio-transport/releases/tag/2.0.0)
+- [gRPC Swift NIO Transport 2.1 (August 2025)](https://github.com/grpc/grpc-swift-nio-transport/releases/tag/2.1.0)
 - [FlatBuffers v25.2.10 (February 2025)](https://github.com/google/flatbuffers/releases/tag/v25.2.10)
 - [Apache Arrow Swift](https://github.com/apache/arrow-swift)