feat: option to disable pre-transform

[antfu]

Description

The pre-transformation is a brilliant optimization to improve the waterfall requests for browsers. But when it's been used for other senario (Vitest, Nuxt, etc.) with lower request overhead, this sometimes could become a negative optimization.

Resolves vitest-dev/vitest#229 (comment)

Additional context

Another option is to provide the option in transformRequest, but that requires a bit complex options passing for plugins and might introduce too much complexity.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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