feat: initial new sonner implementation

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Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. You must list at least one issue. An issue is not required if the PR fixes something trivial like a typo.

Testing this PR

To try this branch, add the following to your pubspec.yaml:

shadcn_ui:
    git:
      url: https://github.com/nank1ro/flutter-shadcn-ui
      ref: your-branch-name-here

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read and followed the Flutter Style Guide.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making.
• I followed the Data Driven Fixes where supported.
• All existing and new tests are passing.
• I bumped the package version following the Semantic Versioning guidelines (For now the major is the second number and the minor the third, because the package is not feature complete). For example, if the package is at version 0.18.0 and you introduced a breaking change or a new feature, bump it to 0.19.0, if you just added a fix or a chore bump it to 0.18.1.
• I updated the CHANGELOG.md file with a summary of changes made following the format already used.

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