chore: move Ed25519 shadow into libs/test-utils module

Consolidates the Ed25519 test shadow from a standalone srcDir into the
existing test-utils module, simplifying the convention plugin to a
single testImplementation dependency.

Author: bmc08gt

build-logic/convention/src/main/kotlin/AndroidEd25519ShadowConventionPlugin.kt

@@ -1,24 +1,12 @@
-import com.android.build.gradle.LibraryExtension
 import org.gradle.api.Plugin
 import org.gradle.api.Project
-import org.gradle.api.artifacts.VersionCatalogsExtension
-import org.gradle.kotlin.dsl.configure
 import org.gradle.kotlin.dsl.dependencies
-import org.gradle.kotlin.dsl.getByType
 
 class AndroidEd25519ShadowConventionPlugin : Plugin<Project> {
     override fun apply(target: Project) {
         with(target) {
-            extensions.configure<LibraryExtension> {
-                sourceSets.getByName("test") {
-                    java.srcDir(rootProject.file("testing/ed25519-shadow"))
-                }
-            }
-
-            val libs = extensions.getByType<VersionCatalogsExtension>().named("libs")
-
             dependencies {
-                "testImplementation"(libs.findLibrary("eddsa").get())
+                "testImplementation"(project(":libs:test-utils"))
             }
         }
     }

libs/test-utils/build.gradle.kts

@@ -7,6 +7,7 @@ android {
 }
 
 dependencies {
+    api(libs.eddsa)
     implementation(libs.kotlinx.coroutines.test)
     implementation(libs.junit)
     implementation(project(":libs:coroutines"))