fix: extract MintPickerItem to fix Kotlin compiler OOM in MintPicker

The deeply-nested Text() call inside DropdownMenu > forEach > DropdownMenuItem
generated bytecode with MAXSTACK=26, which caused java.lang.OutOfMemoryError in
the JVM bytecode frame analyzer (ConstantConditionEliminationMethodTransformer).
Extracting DropdownMenuItem into a top-level private composable breaks the lambda
nesting depth and lets the compiler succeed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmiRNcMEync2rVVbrPzWt

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/CashuWalletScreen.kt

@@ -1234,17 +1234,25 @@ private fun MintPicker(
     }
     DropdownMenu(expanded = expanded, onDismissRequest = { expanded = false }) {
         mints.forEach { m ->
-            DropdownMenuItem(
-                text = { Text(m) },
-                onClick = {
-                    onPick(m)
-                    expanded = false
-                },
-            )
+            MintPickerItem(m) {
+                onPick(m)
+                expanded = false
+            }
         }
     }
 }
 
+@Composable
+private fun MintPickerItem(
+    mint: String,
+    onClick: () -> Unit,
+) {
+    DropdownMenuItem(
+        text = { Text(mint) },
+        onClick = onClick,
+    )
+}
+
 // ============================================================================
 // Send LN (melt)
 // ============================================================================