…test `build`

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

This PR aims to setup `SparkConnect` Swift package structure and CI to test `build`.

Note that this is a subset of the initial implementation.
- #1

### Why are the changes needed?

To setup the initial package structure with CI build test coverage before adding the actual code. Currently, the following two OSs are tested.
- MacOS 15
- Ubuntu 24.04

According to the standard `Swift` package structure,
- https://www.swift.org/getting-started/library-swiftpm/#bootstrapping

this PR adds the following structure for `SparkConnect` package. `SparkConnectError.swift` and `BuilderTests.swift` is added in order to fill the empty directories.
```
$ tree .
.
├── dev
│   └── merge_spark_pr.py
├── LICENSE
├── Package.swift
├── README.md
├── Sources
│   └── SparkConnect
│       └── SparkConnectError.swift
└── Tests
    └── SparkConnectTests
        └── BuilderTests.swift
```

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

No. This is not released yet.

### How was this patch tested?

Pass the CI.

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

No.

Closes #4 from dongjoon-hyun/SPARK-51461.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

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

This PR aims to use `Apache Arrow Swift` 19.0.1. This will be replaced as a dependency when Apache Arrow Swift package is released later.

This is a part of the initial implementation.
- #1

### Why are the changes needed?

Apache Arrow 19.0.1 is the latest version.
- https://arrow.apache.org/release/19.0.1.html (2025-02-16)

Although Apache Arrow 19.0.1 has `Swift` source code,
- For `Arrow` package, we need to change two places to compile in `Swift 6.0` and we need to exclude `ArrowCExporter.swift` and `ArrowCImporter.swift`

```
$ git clone -b apache-arrow-19.0.1 https://github.com/apache/arrow.git
$ cd arrow/swift/Arrow/Sources/Arrow/
$ rm ArrowC*
$ cp * ~/spark-connect-swift/Sources/SparkConnect/
```

```swift
- public enum ArrowTypeId {
+ public enum ArrowTypeId: Sendable {
```

```swift
- public enum Info {
+ public enum Info: Sendable {
```

- For `ArrowFlight` package, we need to update two places to compile in `Swift 6` and use only three files.
  - Flight.pb.swift
  - FlightData.swift
  - FlightDescriptor.swift

```
$ git clone -b apache-arrow-19.0.1 https://github.com/apache/arrow.git
$ cd arrow/swift/ArrowFlight/Sources/ArrowFlight
$ cp Flight.pb.swift FlightData.swift FlightDescriptor.swift ~/spark-connect-swift/Sources/SparkConnect
```

```swift
-  static var allCases: [Arrow_Flight_Protocol_CancelStatus] = [
+  static let allCases: [Arrow_Flight_Protocol_CancelStatus] = [
```

```swift
-  static var allCases: [Arrow_Flight_Protocol_FlightDescriptor.DescriptorType] = [
+  static let allCases: [Arrow_Flight_Protocol_FlightDescriptor.DescriptorType] = [
```

Lastly, `swift format` is applied.
```
$ swift format -i *.swift
```

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

No, this is not released yet.

### How was this patch tested?

Pass the CI.

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

No.

Closes #6 from dongjoon-hyun/SPARK-51465.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

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

This PR aims to add a Swift `SparkConnectClient` actor encapsulating `gRPC` connections which is similar to other language clients.
- Swift (this PR)
```swift
public actor SparkConnectClient {
```

- [Scala](https://github.com/apache/spark/blob/master/sql/connect/common/src/main/scala/org/apache/spark/sql/connect/client/SparkConnectClient.scala):
```scala
private[sql] class SparkConnectClient(
```

- [Python](https://github.com/apache/spark/blob/master/python/pyspark/sql/connect/client/core.py#L597)
```python
class SparkConnectClient(object):
```

This is a part of the following.
- #1

### Why are the changes needed?

To use `gRPC` in the upper `SparkSession` and `DataFrame` layers easily.

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

No, this is not released.

### How was this patch tested?

Pass the CIs.

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

No.

Closes #7 from dongjoon-hyun/SPARK-51472.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>