refactor(counit): use correct type declaration for decoding #51

The `json.decodeFromString` call was incorrectly assigning the result to a variable of type `ExplainQuery` without specifying the generic type. This commit fixes the type declaration to be `json.decodeFromString<ExplainQuery>`, which ensures that the correct type inference is used when decoding the JSON string. This change ensures that the correct type is being used and avoids potential runtime errors.

Author: phodal

src/main/kotlin/cc/unitmesh/devti/counit/CoUnitPreProcessor.kt

@@ -57,8 +57,7 @@ class CoUnitPreProcessor(val project: Project) {
 
             val explain = try {
                 val fixedResult = fix(result)
-                val explain: ExplainQuery = json.decodeFromString(fixedResult)
-                explain
+                json.decodeFromString<ExplainQuery>(fixedResult)
             } catch (e: Exception) {
                 LOG.error("parse result error: $e")
                 return@launch