Add parent span support to tracing examples and tests

Introduce a parent span for the "test" span in README and MainTests.kt to provide a more comprehensive tracing setup. This change ensures that the span hierarchy is clearly established and documented.

README.md

@@ -94,8 +94,11 @@ span.end()
 Similarly to the logging API, we also support a more kotlin style API:
 
 ```kotlin
+// Create the parent span.
+// NOTICE: we do not start it, since it's already started.
+val parent: TracingEvent.Span = trace.span("parent")
 // Starts immediately the span.
-trace.span("test") {
+trace.span("test", parent) {
     // Send events that are related to the current span.
     it.event("this is a test event")
     // Automatically closes at the end of te scope.

log4k/src/commonTest/kotlin/io/github/smyrgeorge/log4k/MainTests.kt

@@ -49,8 +49,11 @@ class MainTests {
             delay(1000)
 
             RootLogger.Tracing.register(SimpleConsoleTracingAppender())
+            // Create the parent span.
+            // NOTICE: we do not start it, since it's already started.
+            val parent: TracingEvent.Span = trace.span("parent")
             // Starts immediately the span.
-            trace.span("test") {
+            trace.span("test", parent) {
                 // Send events that are related to the current span.
                 it.event("this is a test event")
                 // Automatically closes at the end of te scope.