[meta] Flaky tests

[kpavlov]

Describe the bug

Tests are flaky:

• io.modelcontextprotocol.kotlin.sdk.client.StdioClientTransportTest#handle stdio error - green standalone, but is often flaky when running in Gradle (MacOS)
• Additionally, there's a log message: org.gradle.api.GradleException: Could not generate test report to '/home/runner/work/kotlin-sdk/kotlin-sdk/integration-test/build/reports/tests/jsNodeTest'. build. Consider adding pre-step on CI:

  - name: Ensure test report directory exists
    run: mkdir -p kotlin-sdk/integration-test/build/reports/tests/jsNodeTest

• StreamableHttpServerTransportTest
  Details

  [kotlin-sdk-server/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransportTest.kt#L248](https://github.com/modelcontextprotocol/kotlin-sdk/pull/599/files#annotation_47452582818) kotlinx.coroutines.test.UncaughtExceptionsBeforeTest: There were uncaught exceptions before the test started. Please avoid this, as such exceptions are also reported in a platform-dependent manner so that they are not lost.
  https://github.com/modelcontextprotocol/kotlin-sdk/actions/runs/23005812953/attempts/1?pr=599