Port occupied: Clean Logging (#2630)

* test(custom-error): update expected status code from 500 to 400 in custom error handling test

* fix(router): handle `PortOccupiedException` with clear exception propagation

- Added specific handling for `PortOccupiedException` to improve runtime diagnosis and error clarity during router startup.

* fix(router): combine exception handlers into a single block for improved readability and consistency

Author: predic8

core/src/main/java/com/predic8/membrane/core/router/DefaultRouter.java

@@ -165,6 +165,8 @@ public void start() {
             handleDuplicateOpenAPIPaths(e);
         } catch (OpenAPIParsingException e) {
             handleOpenAPIParsingException(e);
+        } catch (PortOccupiedException e) {
+            throw new RuntimeException(e);
         } catch (Exception e) {
             log.error("Could not start router.", e);
             if (e instanceof RuntimeException)