fix: handle resolve optional peer deps

[bluwy]

Description

fix #6007

Introduce __vite-optional-peer-dep prefix (similar to `__vite-browser-external) for packages that are optional peer dependencies.

Additional context

Since knowing optional peer dep requires traversing the parent for package.json, this may incur a small perf cost. But from what I can tell, the logic where I added is rarely called during testing.

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What is the purpose of this pull request?

• [x] Bug fix
• [x] New Feature
• [ ] Documentation update
• [ ] Other

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• [x] Read the Contributing Guidelines.
• [x] Read the Pull Request Guidelines and follow the Commit Convention.
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• [x] Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• [x] Ideally, include relevant tests that fail without this PR but pass with it.