Refactor build.gradle to adjust buildDir paths and ensure evaluation dependencies

- Set `rootProject.buildDir` and configure `subprojects` to use consistent build paths.
- Adjust evaluation dependencies to ensure `:app` is resolved correctly.

Author: anhappdev

flutter/android/build.gradle

@@ -5,22 +5,19 @@ allprojects {
     }
 }
 
+rootProject.buildDir = '../build'
 subprojects {
-   afterEvaluate { project ->
+    project.buildDir = "${rootProject.buildDir}/${project.name}"
+    project.evaluationDependsOn(':app')
+    afterEvaluate { project ->
        if (project.hasProperty('android')) {
            project.android {
                if (namespace == null) {
                    namespace project.group
                }
            }
        }
-   }
-}
-
-rootProject.buildDir = '../build'
-subprojects {
-    project.buildDir = "${rootProject.buildDir}/${project.name}"
-    project.evaluationDependsOn(':app')
+    }
 }
 
 tasks.register("clean", Delete) {