Add streamable HTTP transport for clients (#70)

* Rename file to Transport.swift

* Rename file to StdioTransportTests.swift

* Add .index-build/ to .gitignore

* Implement HTTP client transport

* Add test coverage for streamable HTTP client transport

* Conditionally import FoundationNetworking

* Conditionalize streaming for unsupported platforms

* Import FoundationNetworking in tests

* Add 5 minute timeout to CI jobs

* Remove debug logging

* Formatting

* Skip SSE tests on platforms that don't support streaming

Sources/MCP/Base/Transport.swift

@@ -0,0 +1,20 @@
+import Logging
+
+import struct Foundation.Data
+
+/// Protocol defining the transport layer for MCP communication
+public protocol Transport: Actor {
+    var logger: Logger { get }
+
+    /// Establishes connection with the transport
+    func connect() async throws
+
+    /// Disconnects from the transport
+    func disconnect() async
+
+    /// Sends data
+    func send(_ data: Data) async throws
+
+    /// Receives data in an async sequence
+    func receive() -> AsyncThrowingStream<Data, Swift.Error>
+}