[native_assets_cli] Curate public toplevel functions

[dcharkes]

This PR tries the curate the toplevel functions which are in the public API of what will be package:hooks, package:code_assets and package:data_assets.

The validate functions for the base protocol are moved into a ProtocolBase class. (These need to be public because package:native_assets_builder uses them. And these need to be in package:native_assets_cli because the test methods use them.)

The Dart docs can be inspected by pkgs/native_assets_cli$ dart doc ..

TODOs:

• This PR does not yet curate extension types, and extensions.

Context:

• Work before splitting up the package: [native_assets_cli] Package name #999

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
native_assets_builder	Breaking	0.17.0	0.18.0-wip	0.18.0	✔️
native_assets_cli	Breaking	0.17.0	0.18.0-wip	0.18.0	✔️

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// 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.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
native_assets_builder	Breaking	0.17.0	0.18.0-wip	0.18.0	✔️
native_assets_cli	Breaking	0.17.0	0.18.0-wip	0.18.0	✔️

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// 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.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[goderbauer]

LGTM

[goderbauer]

nit: it's not super clear what "similar" means here? Is this logic that is shared by all/most protocol extensions?

[coveralls]

coverage: 77.838% (-0.02%) from 77.858%
when pulling f10643a on dartdoc-3
into d29f1f4 on main.