refactor(code-highlighting): simplify null checks and return statements

The changes streamline the logic in `CodeBlockHighlightingFilter` and `CodeBlockHighlightErrorFilter` by reducing the number of lines and simplifying the null checks. This results in more concise code that improves readability and maintainability. Specifically, the null checks and early returns have been optimized for better efficiency.

core/src/main/kotlin/cc/unitmesh/devti/gui/snippet/error/CodeBlockHighlightErrorFilter.kt

@@ -7,8 +7,7 @@ import com.intellij.psi.PsiErrorElement
 
 class CodeBlockHighlightErrorFilter : HighlightErrorFilter() {
     override fun shouldHighlightErrorElement(element: PsiErrorElement): Boolean {
-        val containingFile = element.containingFile
-        val highlightedFile = containingFile?.virtualFile ?: return true
+        val highlightedFile = element.containingFile?.virtualFile ?: return true
         return !AutoDevSnippetFile.isSnippet(highlightedFile)
     }
 }

core/src/main/kotlin/cc/unitmesh/devti/gui/snippet/error/CodeBlockHighlightingFilter.kt

@@ -11,13 +11,9 @@ import com.intellij.psi.PsiFile
 class CodeBlockHighlightingFilter : HighlightInfoFilter {
     override fun accept(highlightInfo: HighlightInfo, file: PsiFile?): Boolean {
         val hasError = highlightInfo.severity >= HighlightSeverity.GENERIC_SERVER_ERROR_OR_WARNING;
+        if (file == null || !hasError) return true
+        val virtualFile = file.virtualFile ?: return true
 
-        if (file == null || !hasError) {
-            return true;
-        }
-
-        val virtualFile = file.virtualFile;
-
-        return !(virtualFile != null && AutoDevSnippetFile.isSnippet(virtualFile));
+        return !(AutoDevSnippetFile.isSnippet(virtualFile))
     }
 }