feat(characters:data): DTOs, mappers, data source, repo, Koin module (REDI-86)

- @Serializable CharacterDto/CharactersResponseDto/PageInfoDto in dto/.
- mappers/CharacterMapper.kt: internal, pure toDomain()/toCharacter()/toCharacterDetails();
  nextPage parsed from info.next URL. No mapping inside DTO/data-source classes.
- KtorCharacterDataSource via the typed HttpClient.get helpers (errors -> DataError.Network).
- NetworkCharacterRepository (not *Impl) maps DTO -> domain; DataError.Network widens to DataError.
- charactersDataModule: singleOf(::KtorCharacterDataSource) + singleOf(::NetworkCharacterRepository) { bind<CharacterRepository>() }.
- core:data: expose ktor-client-core as api (public inline helpers are inlined into consumers) and
  move Timber logging into a @PublishedApi internal fn so Timber doesn't leak across modules.

core/data/src/main/kotlin/com/example/architecture/core/data/network/HttpClientExt.kt

@@ -65,21 +65,31 @@ suspend inline fun <reified T> safeCall(
     return try {
         responseToResult(execute())
     } catch (e: UnresolvedAddressException) {
-        Timber.tag("HttpClient").e(e, "No internet (unresolved address)")
+        logNetworkError(e, "No internet (unresolved address)")
         Result.Error(DataError.Network.NO_INTERNET)
     } catch (e: UnknownHostException) {
-        Timber.tag("HttpClient").e(e, "No internet (unknown host)")
+        logNetworkError(e, "No internet (unknown host)")
         Result.Error(DataError.Network.NO_INTERNET)
     } catch (e: SerializationException) {
-        Timber.tag("HttpClient").e(e, "Serialization failure")
+        logNetworkError(e, "Serialization failure")
         Result.Error(DataError.Network.SERIALIZATION)
     } catch (e: Exception) {
         if (e is CancellationException) throw e
-        Timber.tag("HttpClient").e(e, "Unknown network failure")
+        logNetworkError(e, "Unknown network failure")
         Result.Error(DataError.Network.UNKNOWN)
     }
 }
 
+/**
+ * Logs a caught network error. `@PublishedApi internal` so the public inline [safeCall] can call it
+ * across modules WITHOUT leaking Timber: the Timber dependency stays inside `:core:data` because
+ * this function's body is not inlined into the caller.
+ */
+@PublishedApi
+internal fun logNetworkError(throwable: Throwable, message: String) {
+    Timber.tag("HttpClient").e(throwable, message)
+}
+
 /** Maps HTTP status codes to typed [DataError.Network] (extends the skill table with 400/403/404). */
 suspend inline fun <reified T> responseToResult(
     response: HttpResponse,