Refactor StdioClientTransport tests

Author: kpavlov

kotlin-sdk-client/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/stdio/StdioClientTransportErrorHandlingTest.kt renamed to kotlin-sdk-client/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/stdio/StdioClientTransportErrorHandlingTest.kt

@@ -3,12 +3,12 @@ package io.modelcontextprotocol.kotlin.sdk.client.stdio
 import io.kotest.matchers.booleans.shouldBeFalse
 import io.kotest.matchers.shouldBe
 import io.modelcontextprotocol.kotlin.sdk.client.StdioClientTransport
-import kotlinx.atomicfu.atomic
-import kotlinx.atomicfu.update
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
 import kotlinx.io.Buffer
 import kotlinx.io.writeString
+import kotlin.concurrent.atomics.AtomicBoolean
+import kotlin.concurrent.atomics.ExperimentalAtomicApi
 import kotlin.test.Test
 import kotlin.time.Duration.Companion.milliseconds
 
@@ -19,6 +19,7 @@ class StdioClientTransportErrorHandlingTest {
 
     private lateinit var transport: StdioClientTransport
 
+    @OptIn(ExperimentalAtomicApi::class)
     @Test
     fun `should continue on stderr EOF`() = runTest {
         val stderrBuffer = Buffer()
@@ -34,17 +35,17 @@ class StdioClientTransportErrorHandlingTest {
             error = stderrBuffer,
         )
 
-        val closeCalled = atomic(false)
-        transport.onClose { closeCalled.update { true } }
+        val closeCalled = AtomicBoolean(false)
+        transport.onClose { closeCalled.store(true) }
 
         transport.start()
         delay(200.milliseconds)
 
         // Stderr EOF should not close transport
-        closeCalled.value shouldBe false
+        closeCalled.load() shouldBe false
 
         transport.close()
-        closeCalled.value shouldBe true
+        closeCalled.load() shouldBe true
     }
 
     @Test