fix(download): stop crashing native finalization on Android regex

Android's regex engine rejects Pattern.UNICODE_CHARACTER_CLASS, so NativeFinalizationPolicy failed to initialize and every native download crashed while writing metadata. List Unicode spaces explicitly and cover the separator with a device test.

android/app/src/androidTest/kotlin/com/zarz/spotiflac/NativeFinalizationPolicyDeviceTest.kt

@@ -0,0 +1,30 @@
+package com.zarz.spotiflac
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * Runs on Android's own regex engine: the JVM accepts regex flags that the
+ * device rejects when NativeFinalizationPolicy initializes during finalization.
+ */
+@RunWith(AndroidJUnit4::class)
+class NativeFinalizationPolicyDeviceTest {
+    @Test
+    fun primaryArtistSeparatorCompilesAndSplitsOnDevice() {
+        for ((input, expected) in listOf(
+            "Calle 24, Chino Pacas" to "Calle 24",
+            "Artist A feat. Artist B" to "Artist A",
+            "Artist A\u00A0feat.\u00A0Artist B" to "Artist A",
+            "Artist A\u3000x\u3000Artist B" to "Artist A",
+            "Malcolm X" to "Malcolm X",
+        )) {
+            assertEquals(input, expected, NativeFinalizationPolicy.artistTagValue(input, "primary"))
+        }
+        assertEquals(
+            "Artist A, Artist B",
+            NativeFinalizationPolicy.artistTagValue("Artist A, Artist B", "joined"),
+        )
+    }
+}

android/app/src/main/kotlin/com/zarz/spotiflac/NativeFinalizationPolicy.kt

@@ -1,7 +1,6 @@
 package com.zarz.spotiflac
 
 import java.util.Locale
-import java.util.regex.Pattern
 import kotlin.math.roundToInt
 
 /**
@@ -374,12 +373,17 @@ internal object NativeFinalizationPolicy {
             ?: ""
     }
 
-    // Same separator set as the Rust writer and Dart's primaryArtistTagValue;
-    // Unicode classes keep \s aligned with their whitespace handling.
-    private val primaryArtistSeparator = Pattern.compile(
-        "\\s*[,;&]\\s*|\\s+x\\s+|\\s+(?:feat(?:uring)?|ft|with)\\.?(?:\\s+|$)",
-        Pattern.CASE_INSENSITIVE or Pattern.UNICODE_CHARACTER_CLASS,
-    ).toRegex()
+    // Same separator set as the Rust writer and Dart's primaryArtistTagValue.
+    // Android's regex engine rejects Pattern.UNICODE_CHARACTER_CLASS when this
+    // object initializes, so Unicode spaces are listed explicitly instead.
+    private const val PRIMARY_ARTIST_SPACE = "[\\s\\p{Z}]"
+    private val primaryArtistSeparator = Regex(
+        "$PRIMARY_ARTIST_SPACE*[,;&]$PRIMARY_ARTIST_SPACE*" +
+            "|$PRIMARY_ARTIST_SPACE+x$PRIMARY_ARTIST_SPACE+" +
+            "|$PRIMARY_ARTIST_SPACE+(?:feat(?:uring)?|ft|with)\\.?" +
+            "(?:$PRIMARY_ARTIST_SPACE+|$)",
+        RegexOption.IGNORE_CASE,
+    )
 
     /**
      * Artist tag value for [mode]. Only "primary" changes the value: the first

android/app/src/test/kotlin/com/zarz/spotiflac/NativeFinalizationPolicyTest.kt

@@ -21,6 +21,8 @@ class NativeFinalizationPolicyTest {
             "Artist A with Artist B" to "Artist A",
             "Artist A x Artist B" to "Artist A",
             "Artist A X Artist B" to "Artist A",
+            "Artist A\u00A0feat.\u00A0Artist B" to "Artist A",
+            "Artist A\u3000x\u3000Artist B" to "Artist A",
             " , Artist A, Artist B" to "Artist A",
             "Malcolm X" to "Malcolm X",
             "Artist Without Fear" to "Artist Without Fear",