Rename the example file names related to SSE.

This PR renamed the files related to the SSE example and fixed the README.md.
Because missing files were specified in README.md.

And also, I removed the word 'test' from the file names related to the SSE example.
Other examples file names do not contain the word `test`.

Author: dak2

examples/README.md

@@ -57,7 +57,7 @@ The client will demonstrate:
 - Listing and reading resources
 - Session cleanup
 
-### 4. SSE Test Server (`sse_test_server.rb`)
+### 4. Streamable HTTP Server (`streamable_http_server.rb`)
 A specialized HTTP server designed to test and demonstrate Server-Sent Events (SSE) functionality in the MCP protocol.
 
 **Features:**
@@ -71,12 +71,12 @@ A specialized HTTP server designed to test and demonstrate Server-Sent Events (S
 
 **Usage:**
 ```bash
-ruby examples/sse_test_server.rb
+ruby examples/streamable_http_server.rb
 ```
 
 The server will start on `http://localhost:9393` and provide detailed instructions for testing SSE functionality.
 
-### 5. SSE Test Client (`sse_test_client.rb`)
+### 5. Streamable HTTP Client (`streamable_http_client.rb`)
 An interactive client that connects to the SSE stream and provides a menu-driven interface for testing SSE functionality.
 
 **Features:**
@@ -88,12 +88,12 @@ An interactive client that connects to the SSE stream and provides a menu-driven
 **Usage:**
 1. Start the SSE test server in one terminal:
    ```bash
-   ruby examples/sse_test_server.rb
+   ruby examples/streamable_http_server.rb
    ```
 
 2. Run the SSE test client in another terminal:
    ```bash
-   ruby examples/sse_test_client.rb
+   ruby examples/streamable_http_client.rb
    ```
 
 The client will: