feat: add macOS native targets (macosX64, macosArm64) to quartz

- Declare macosX64() and macosArm64() KMP targets in build.gradle.kts
- Wire macosMain/macosTest source sets through appleMain/appleTest
- Move Secp256k1NativeBenchmark from linuxX64Test to nativeTest so it
  runs on all native targets (Linux, macOS, iOS)
- Use platform() for dynamic labels instead of hardcoded "linuxX64"
- Update run_all.sh to pick the correct native target per OS/arch

https://claude.ai/code/session_01WSNE6QKiYM2ZutQD2UihCW

quartz/build.gradle.kts

@@ -87,6 +87,9 @@ kotlin {
 
     linuxX64()
 
+    macosX64()
+    macosArm64()
+
     // This makes sure that the resource file directory is visible for iOS tests.
     val rootDir = "${rootProject.rootDir.path}/quartz/src/commonTest/resources"
 
@@ -297,6 +300,32 @@ kotlin {
             dependsOn(iosTest.get())
         }
 
+        val macosMain =
+            create("macosMain") {
+                dependsOn(appleMain)
+            }
+
+        val macosTest =
+            create("macosTest") {
+                dependsOn(appleTest)
+            }
+
+        val macosX64Main by getting {
+            dependsOn(macosMain)
+        }
+
+        val macosX64Test by getting {
+            dependsOn(macosTest)
+        }
+
+        val macosArm64Main by getting {
+            dependsOn(macosMain)
+        }
+
+        val macosArm64Test by getting {
+            dependsOn(macosTest)
+        }
+
         val linuxMain =
             create("linuxMain") {
                 dependsOn(nativeMain)