refactor: rename package fai_client_sdk -> chain_client_sdk

The SDK belongs to the Ch∆In product, not the F∆I vendor namespace
(a future Brain client SDK would otherwise collide). Rename the Dart
package, entry library, test + example files. Also drop a private
project name from a doc comment. dart analyze: clean.

Dependents must update their dependency name + package: imports.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

example/chain_client_sdk_example.dart

@@ -0,0 +1,18 @@
+// Example: connect to a locally-running F∆I hub.
+//
+// Run with `dart run example/chain_client_sdk_example.dart`.
+
+import 'package:chain_client_sdk/chain_client_sdk.dart';
+
+Future<void> main() async {
+  final client = HubClient(
+    endpoint: const HubEndpoint(host: '127.0.0.1', port: 50051),
+  );
+
+  // ignore: avoid_print
+  print('would connect to ${client.endpoint}');
+  // ignore: avoid_print
+  print('(SDK is a stub today; live RPC arrives with codegen)');
+
+  await client.close();
+}