fix(build): expose kotlinx-coroutines to consumers

SamsungHealthObserver.observe returns a Flow, but kotlinx-coroutines-android
was an implementation dependency, published with runtime scope, so apps
couldn't compile calls to observe(). A probe module depending only on the
published library found it, and JitPack's POM for 18b2246 confirms the
runtime scope.

Changes:
- library/build.gradle.kts: kotlinx-coroutines-android as api

Tests: the published POM lists kotlinx-coroutines-android with compile scope;
a consumer module without the Samsung SDK now compiles read, aggregate,
insert, requestPermissions and observe calls; 67 unit tests, apiCheck and
ktlint green.

Author: kvs-coder

library/build.gradle.kts

@@ -57,7 +57,8 @@ kotlin {
 dependencies {
     // Samsung's license forbids redistribution: consumers add the AAR themselves.
     compileOnly(samsungHealthData)
-    implementation(libs.kotlinx.coroutines.android)
+    // api: Flow is part of the public API (SamsungHealthObserver.observe).
+    api(libs.kotlinx.coroutines.android)
     api(libs.kotlinx.serialization.json)
 
     testImplementation(samsungHealthData)