Add experimental mcpClient(...) factory method (#396)

- Introduced `@ExperimentalMcpApi` annotation to mark experimental APIs.
- Added `mcpClient` function for initializing and connecting MCP
clients.
- Modified tests to utilize the new `mcpClient` function.
- Refactored variable naming in transport tests for improved
readability.

## Motivation and Context
To improve the creation of the MCP Client experience.

## How Has This Been Tested?
Integration test updated

## Breaking Changes
No

## 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
- [x] 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-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/ExperimentalMcpApi.kt

@@ -0,0 +1,54 @@
+package io.modelcontextprotocol.kotlin.sdk
+
+import kotlin.annotation.AnnotationTarget.ANNOTATION_CLASS
+import kotlin.annotation.AnnotationTarget.CLASS
+import kotlin.annotation.AnnotationTarget.CONSTRUCTOR
+import kotlin.annotation.AnnotationTarget.FIELD
+import kotlin.annotation.AnnotationTarget.FUNCTION
+import kotlin.annotation.AnnotationTarget.LOCAL_VARIABLE
+import kotlin.annotation.AnnotationTarget.PROPERTY
+import kotlin.annotation.AnnotationTarget.PROPERTY_GETTER
+import kotlin.annotation.AnnotationTarget.PROPERTY_SETTER
+import kotlin.annotation.AnnotationTarget.TYPEALIAS
+import kotlin.annotation.AnnotationTarget.VALUE_PARAMETER
+
+/**
+ * Annotation marking an API as experimental and subject to changes or removal in the future.
+ *
+ * This annotation is used to signal that a particular element, such as a class, function, or property,
+ * is part of an experimental API. Such APIs may not be stable, and their usage requires opting in
+ * explicitly.
+ *
+ * Users of the annotated API must explicitly accept the opt-in requirement to ensure they are aware
+ * of the potential instability or unfinished nature of the API.
+ *
+ * Targets that can be annotated include:
+ * - Classes
+ * - Annotation classes
+ * - Properties
+ * - Fields
+ * - Local variables
+ * - Value parameters
+ * - Constructors
+ * - Functions
+ * - Property getters
+ * - Property setters
+ * - Type aliases
+ */
+@RequiresOptIn
+@MustBeDocumented
+@Target(
+    CLASS,
+    ANNOTATION_CLASS,
+    PROPERTY,
+    FIELD,
+    LOCAL_VARIABLE,
+    VALUE_PARAMETER,
+    CONSTRUCTOR,
+    FUNCTION,
+    PROPERTY_GETTER,
+    PROPERTY_SETTER,
+    TYPEALIAS,
+)
+@Retention(AnnotationRetention.BINARY)
+public annotation class ExperimentalMcpApi