Add convenience constructors to JSONRPCRequest (#336)

- Add convenience constructors to JSONRPCRequest
- Make UUID string a default JSONRPCRequest

## Motivation and Context
To create request objects more easily

## How Has This Been Tested?
Unit tests

## Breaking Changes
No, this is a new API

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

kotlin-sdk-client/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/StreamableHttpClientTransportTest.kt

@@ -17,7 +17,6 @@ import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCMessage
 import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCNotification
 import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCRequest
 import io.modelcontextprotocol.kotlin.sdk.types.McpJson
-import io.modelcontextprotocol.kotlin.sdk.types.RequestId
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
@@ -50,7 +49,7 @@ class StreamableHttpClientTransportTest {
     @Test
     fun testSendJsonRpcMessage() = runTest {
         val message = JSONRPCRequest(
-            id = RequestId.StringId("test-id"),
+            id = "test-id",
             method = "test",
             params = buildJsonObject { },
         )
@@ -78,7 +77,7 @@ class StreamableHttpClientTransportTest {
     @Test
     fun testStoreSessionId() = runTest {
         val initMessage = JSONRPCRequest(
-            id = RequestId.StringId("test-id"),
+            id = "test-id",
             method = "initialize",
             params = buildJsonObject {
                 put(