[record_use] Remove internal fromJson and toJson

[dcharkes]

This PR only leaves the top level Recordings and RecordedUsages JSON APIs. All internal from and to json have been removed.

The format uses normalization (with constant indices), which means the to and from JSON of parts of the format are not useful by themselves. Users should not try to use JSON serialization of parts of the format, only the full format.

Closes: #2901

This will require a manual roll into the Dart SDK to migrate Metadata.fromJson constructor calls.

[github-actions]

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// Copyright (c) 2026, 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/hooks_runner/test_data/download_assets/hook/build.dart
pkgs/jni/test/debug_release_test.dart
pkgs/objective_c/example/command_line/lib/main.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

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Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
record_use	Breaking	0.4.2	0.5.0-wip	0.5.0	✔️

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[github-actions]

PR Health

License Headers ✔️

// Copyright (c) 2026, 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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no missing headers

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pkgs/hooks_runner/test_data/download_assets/hook/build.dart
pkgs/jni/test/debug_release_test.dart
pkgs/objective_c/example/command_line/lib/main.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

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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.

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Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
record_use	Breaking	0.4.2	0.5.0-wip	0.5.0	✔️

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[goderbauer]

LGTM

[coveralls]

coverage: 81.81% (+0.1%) from 81.707%
when pulling 646c9a8 on json-private
into c26f756 on main.