feat: expose verifySchnorrFast in Secp256k1InstanceOurs + Android benchmark

Wire verifySchnorrFast (x-check only, no y-parity inversion) into:
- Secp256k1InstanceOurs wrapper for app-level usage
- Android benchmark as verifySchnorrFastOurs for Pixel 8 measurement

Expected: ~15% faster than verifySchnorrOurs (~100μs vs ~120μs on Pixel 8)

https://claude.ai/code/session_01EMY5RnXb9rnsyU2KbXrSaY

benchmark/src/androidTest/java/com/vitorpamplona/quartz/benchmark/Secp256k1Benchmark.kt

@@ -123,6 +123,13 @@ class Secp256k1Benchmark {
         }
     }
 
+    @Test
+    fun verifySchnorrFastOurs() {
+        benchmarkRule.measureRepeated {
+            assertTrue(Secp256k1InstanceOurs.verifySchnorrFast(signature, msg32, xOnlyPub))
+        }
+    }
+
     @Test
     fun signSchnorrOurs() {
         benchmarkRule.measureRepeated {

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/Secp256k1InstanceOurs.kt

@@ -62,6 +62,16 @@ object Secp256k1InstanceOurs {
         pubKey: ByteArray,
     ): Boolean = Secp256k1.verifySchnorr(signature, hash, pubKey)
 
+    /**
+     * Fast Nostr verify — skips BIP-340 y-parity inversion (~15% faster).
+     * Safe for Nostr event verification. See Secp256k1.verifySchnorrFast KDoc.
+     */
+    fun verifySchnorrFast(
+        signature: ByteArray,
+        hash: ByteArray,
+        pubKey: ByteArray,
+    ): Boolean = Secp256k1.verifySchnorrFast(signature, hash, pubKey)
+
     fun privateKeyAdd(
         first: ByteArray,
         second: ByteArray,