test(quartz/utils): add GZipTest to commonTest

Covers the full expect/actual contract across all platforms (Android,
JVM, iOS):

- round-trip for empty, single-char, simple, unicode, and JSON strings
- repetitive input compresses to a smaller size
- gzip magic number (0x1F 0x8B) present in compressed output
- compressed bytes differ from raw input bytes
- decompress of invalid data throws an exception
- special/control characters survive a round-trip

https://claude.ai/code/session_0125CGfu6aMAnSv6ZzAxFHvV

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/utils/GZipTest.kt

@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.utils
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFails
+import kotlin.test.assertTrue
+
+class GZipTest {
+    @Test
+    fun roundTripSimpleString() {
+        val original = "Hello, Nostr!"
+        val decompressed = GZip.decompress(GZip.compress(original))
+        assertEquals(original, decompressed)
+    }
+
+    @Test
+    fun roundTripEmptyString() {
+        val original = ""
+        val decompressed = GZip.decompress(GZip.compress(original))
+        assertEquals(original, decompressed)
+    }
+
+    @Test
+    fun roundTripLongRepetitiveString() {
+        val original = "abcdefghij".repeat(1000)
+        val compressed = GZip.compress(original)
+        val decompressed = GZip.decompress(compressed)
+        assertEquals(original, decompressed)
+    }
+
+    @Test
+    fun compressedSizeIsSmallerForRepetitiveInput() {
+        val original = "abcdefghij".repeat(1000)
+        val compressed = GZip.compress(original)
+        assertTrue(
+            compressed.size < original.encodeToByteArray().size,
+            "Expected compressed size (${compressed.size}) to be smaller than original (${original.encodeToByteArray().size})",
+        )
+    }
+
+    @Test
+    fun roundTripUnicodeString() {
+        val original = "こんにちは世界 🌍 مرحبا Привет"
+        val decompressed = GZip.decompress(GZip.compress(original))
+        assertEquals(original, decompressed)
+    }
+
+    @Test
+    fun roundTripNostrJsonEvent() {
+        val original =
+            """{"id":"abc123","pubkey":"deadbeef","created_at":1700000000,"kind":1,""" +
+                """"tags":[],"content":"Hello world","sig":"cafebabe"}"""
+        val decompressed = GZip.decompress(GZip.compress(original))
+        assertEquals(original, decompressed)
+    }
+
+    @Test
+    fun compressedBytesStartWithGzipMagicNumber() {
+        // gzip streams always begin with 0x1F 0x8B
+        val compressed = GZip.compress("test")
+        assertTrue(compressed.size >= 2, "Compressed output too short to contain gzip header")
+        assertEquals(0x1F.toByte(), compressed[0], "Expected gzip magic byte 0 (0x1F)")
+        assertEquals(0x8B.toByte(), compressed[1], "Expected gzip magic byte 1 (0x8B)")
+    }
+
+    @Test
+    fun compressedOutputDiffersFromInput() {
+        val original = "Hello, Nostr!"
+        val compressed = GZip.compress(original)
+        assertTrue(
+            !compressed.contentEquals(original.encodeToByteArray()),
+            "Compressed output should differ from the raw input bytes",
+        )
+    }
+
+    @Test
+    fun decompressInvalidDataThrows() {
+        val garbage = byteArrayOf(0x00, 0x01, 0x02, 0x03, 0x04)
+        assertFails { GZip.decompress(garbage) }
+    }
+
+    @Test
+    fun roundTripSingleCharacter() {
+        val original = "A"
+        assertEquals(original, GZip.decompress(GZip.compress(original)))
+    }
+
+    @Test
+    fun roundTripSpecialCharacters() {
+        val original = "\t\n\r\u0000\u001F\u007F"
+        assertEquals(original, GZip.decompress(GZip.compress(original)))
+    }
+}