Fix dart analyze and format on 3.7.0

[ntkme]

This PR fixes the following:

warning • lib/src/deprecation.dart:185:43 • A value for optional parameter 'description' isn't ever given. Try removing the unused parameter. • unused_element_parameter
   info • lib/sass.dart:6:9 • Library names are not necessary. Remove the library name. • unnecessary_library_name
   info • pkg/sass_api/lib/sass_api.dart:6:9 • Library names are not necessary. Remove the library name. • unnecessary_library_name

There are a few deprecated_member_use on dart:js_util, but migrate to dart:js is not a small task so that I'm not touching those for now.

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For dart format this PR adds dart pub get before running dart format in CI to make sure the language version is correctly detected and a consistent format is produced.

[ntkme]

@nex3 I just found out that with dart 3.7, if you start with a clean clone of the repo (or run git clean -dffx), it formats in one way. Then, after running dart pub get, it formats in another way...

[ntkme]

It's mentioned in the changelog: https://github.com/dart-lang/sdk/blob/main/CHANGELOG.md#dart-format

In order to correctly determine the language version of each file it formats, dart format (like other dart commands) looks for a package_config.json file surrounding the files being formatted. This means that you need to run dart pub get before formatting code in your package. If you have format checks in your continuous integration server, you'll want to make sure it runs dart pub get too.