build: restore upstream's Gradle 10 source-set cleanup in quartz after the merge

The merge of origin/main resolved quartz/build.gradle.kts with the branch
side wholesale, which kept the shared purity-gate apply but dropped the
`by getting` -> `getByName(...)` cleanup from 6e3af61e. Re-applied on top.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N56KzPSYiN5edMRamvKEgD

quartz/build.gradle.kts

@@ -304,11 +304,11 @@ kotlin {
             dependsOn(appleMain)
         }
 
-        val iosArm64Main by getting {
+        getByName("iosArm64Main") {
             dependsOn(iosMain.get())
         }
 
-        val iosSimulatorArm64Main by getting {
+        getByName("iosSimulatorArm64Main") {
             dependsOn(iosMain.get())
         }
 
@@ -316,11 +316,11 @@ kotlin {
             dependsOn(appleTest)
         }
 
-        val iosArm64Test by getting {
+        getByName("iosArm64Test") {
             dependsOn(iosTest.get())
         }
 
-        val iosSimulatorArm64Test by getting {
+        getByName("iosSimulatorArm64Test") {
             dependsOn(iosTest.get())
         }
 
@@ -334,11 +334,11 @@ kotlin {
                 dependsOn(appleTest)
             }
 
-        val macosArm64Main by getting {
+        getByName("macosArm64Main") {
             dependsOn(macosMain)
         }
 
-        val macosArm64Test by getting {
+        getByName("macosArm64Test") {
             dependsOn(macosTest)
         }
 
@@ -355,11 +355,11 @@ kotlin {
                 dependsOn(nativeTest)
             }
 
-        val linuxX64Main by getting {
+        getByName("linuxX64Main") {
             dependsOn(linuxMain)
         }
 
-        val linuxX64Test by getting {
+        getByName("linuxX64Test") {
             dependsOn(linuxTest)
         }
     }