refactor(geode): test fixtures + collectUntilEose helper, move to testFixtures sourceSet

The in-process relay was usable but every consumer test paid a 10–15
line tax for scope/client setup, manual cleanup inside the test body
(leaks on assertion failure), hardcoded "ws://127.0.0.1:7770/" magic
strings, and an inline collectUntilEose pattern reinvented per file.

Net: ~250 LOC removed, every test gets correct @After cleanup, and
the synthetic event builders no longer ship in geode's production jar.

- Move geode.fixtures (synthetic event builders) and the new
  geode.testing package from src/main to a new src/testFixtures
  source set via the java-test-fixtures plugin. Production geode jar
  no longer includes them; consumers wire them with
  testImplementation(testFixtures(project(":geode"))).
- Add geode.testing.RelayClientTest open class — owns hub, scope,
  client, defaultRelay, defaultRelayUrl with @After-driven cleanup.
- Add geode.testing.collectUntilEose / collectUntilEoseMulti
  NostrClient extensions with a shared subId counter and timeout knob.
  Replaces hand-rolled subscriber loops in 4+ files.
- Add RelayHub.DEFAULT_URL constant so tests stop typing
  "ws://127.0.0.1:7770/" inline.
- Migrate the 8 quartz NostrClient*Test files + geode's
  Nip01ComplianceTest to extend RelayClientTest and (where REQ/EOSE
  is the pattern) call collectUntilEose. Delete the redundant
  BaseNostrClientTest wrapper.

geode/build.gradle.kts

@@ -4,6 +4,7 @@ plugins {
     alias(libs.plugins.jetbrainsKotlinJvm)
     alias(libs.plugins.serialization)
     application
+    `java-test-fixtures`
 }
 
 application {
@@ -25,6 +26,15 @@ sourceSets {
     test {
         kotlin.srcDir("src/test/kotlin")
     }
+    // The `java-test-fixtures` plugin auto-creates a `testFixtures`
+    // source set; we just point it at our Kotlin layout so the
+    // `geode.fixtures` (synthetic events) and `geode.testing`
+    // (RelayClientTest, collectUntilEose) packages don't ship in
+    // production jars but are still usable by every consumer's test
+    // source via `testImplementation(testFixtures(project(":geode")))`.
+    named("testFixtures") {
+        kotlin.srcDir("src/testFixtures/kotlin")
+    }
 }
 
 tasks.withType<Test>().configureEach {
@@ -63,6 +73,13 @@ dependencies {
     // port their configs nearly verbatim.
     implementation(libs.fourkoma)
 
+    // testFixtures: code in src/testFixtures/kotlin (RelayClientTest +
+    // synthetic event builders). Not shipped in the production jar but
+    // exposed to consumers via testImplementation(testFixtures(...)).
+    testFixturesApi(project(":quartz"))
+    testFixturesApi(libs.junit)
+    testFixturesImplementation(libs.kotlinx.coroutines.core)
+
     testImplementation(libs.kotlin.test)
     testImplementation(libs.kotlinx.coroutines.test)
     testImplementation(libs.secp256k1.kmp.jni.jvm)