Merge `package:characters`

[mosuem]

• [x] Move and fix workflow files and badges in the README.md
• [x] Update pubspec.yaml to point to the new repository
• [x] Rev the version of the package, so that pub.dev points to the correct site
• [x] Add the package to the top-level readme of the monorepo
• [x] Important! Merge the PR with 'Create a merge commit' (enabling then disabling the Allow merge commits admin setting)
• [x] Update the auto-publishing settings on https://pub.dev/packages/characters/admin
• [x] Add the following text to https://github.com/dart-lang/characters/:'

> [!IMPORTANT]  
> This repo has moved to https://github.com/dart-lang/core/tree/main/pkgs/characters

• [x] Publish using the autopublish workflow
• [x] Push tags to GitHub using git tag --list 'characters*' | xargs git push origin
• [x] Close open PRs in dart-lang/characters with the following message:

Closing as the [dart-lang/characters](https://github.com/dart-lang/characters) repository is merged into the [dart-lang/core](https://github.com/dart-lang/core) monorepo. Please re-open this PR there!

• [x] Transfer issues by running dart run pkgs/repo_manage/bin/report.dart transfer-issues --source-repo dart-lang/characters --target-repo dart-lang/core --add-label package-characters --apply-changes
• [ ] Archive https://github.com/dart-lang/characters/

---

• [x] I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

- See our [contributor guide](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md) for general expectations for PRs. - Larger or significant changes should be discussed in an issue before creating a PR. - Contributions to our repos should follow the [Dart style guide](https://dart.dev/guides/language/effective-dart) and use `dart format`. - Most changes should add an entry to the changelog and may need to [rev the pubspec package version](https://github.com/dart-lang/sdk/blob/main/docs/External-Package-Maintenance.md#making-a-change). - Changes to packages require [corresponding tests](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md#Testing). Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[github-actions[bot]]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:characters	1.3.1	ready to publish	characters-v1.3.1
package:args	2.6.1-wip	WIP (no publish necessary)
package:async	2.12.0	already published at pub.dev
package:convert	3.1.2	already published at pub.dev
package:crypto	3.0.6	already published at pub.dev
package:fixnum	1.1.1	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions[bot]]

PR Health

Changelog Entry :heavy_check_mark:

| Package | Changed Files | | :--- | :--- | Changes to files need to be [accounted for](https://github.com/dart-lang/ecosystem/wiki/Changelog) in their respective changelogs.

Coverage :warning:

| File | Coverage | | :--- | :--- | |pkgs/characters/benchmark/benchmark.dart| :broken_heart: Not covered | |pkgs/characters/example/main.dart| :broken_heart: Not covered | |pkgs/characters/lib/characters.dart| :broken_heart: Not covered | |pkgs/characters/lib/src/characters.dart| :green_heart: 100 % | |pkgs/characters/lib/src/characters_impl.dart| :green_heart: 89 % | |pkgs/characters/lib/src/extensions.dart| :broken_heart: 0 % :arrow_down: NaN % | |pkgs/characters/lib/src/grapheme_clusters/breaks.dart| :green_heart: 97 % | |pkgs/characters/lib/src/grapheme_clusters/constants.dart| :broken_heart: Not covered | |pkgs/characters/lib/src/grapheme_clusters/table.dart| :green_heart: 100 % | |pkgs/characters/tool/benchmark.dart| :broken_heart: Not covered | |pkgs/characters/tool/bin/gentable.dart| :broken_heart: Not covered | |pkgs/characters/tool/bin/gentest.dart| :broken_heart: Not covered | |pkgs/characters/tool/generate.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/args.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/atsp.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/automaton_builder.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/data_files.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/grapheme_category_loader.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/indirect_table.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/list_overlap.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/shared.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/string_literal_writer.dart| :broken_heart: Not covered | |pkgs/characters/tool/src/table_builder.dart| :broken_heart: Not covered | This check for [test coverage](https://github.com/dart-lang/ecosystem/wiki/Test-Coverage) is informational (issues shown here will not fail the PR). This check can be disabled by tagging the PR with `skip-coverage-check`.

API leaks :heavy_check_mark:

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 :heavy_check_mark:

``` // Copyright (c) 2024, 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](https://github.com/dart-lang/ecosystem/wiki/License-Header).