[hooks] Point to code assets examples

[dcharkes]

Make the examples/README.md of package:hooks point to the examples from package:code_assets.

Note: I don't know if the relative paths to outside the package work properly, if not we'll need to use absolute URLs.

Bug:

• [hooks] Clean up examples #2686

[coveralls]

coverage: 81.228%. remained the same
when pulling 5724cb5 on hooks-examples
into c76ea57 on main.

[github-actions]

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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pkgs/objective_c/lib/src/ns_input_stream.dart

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[goderbauer]

LGTM