@utility doesn't allow for escaped utility names

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What version of Tailwind CSS are you using?

v4.1.18

Reproduction URL

https://play.tailwindcss.com/LrHsRLSUuF?file=css

Describe your issue

The @utility function allows you to create utilities with special characters in them like a forward slash and it will automatically escape them (@utility my/utility { ... } -> .my\/utility { ... })

However, if you pass it an already escaped utility name, it will throw an error:

`@utility my\/utility` defines an invalid utility name. Utilities should be alphanumeric and start with a lowercase letter.

This is a problem as some linters like biome will correctly fail to parse the unescaped forward slash version, as it's not valid css: https://biomejs.dev/playground/?code=QAB1AHQAaQBsAGkAdAB5ACAAbQB5AC8AdQB0AGkAbABpAHQAeQAgAHsACgAgACAAYwBvAGwAbwByADoAIAByAGUAZAA7AAoAfQA%3D&language=css

Best solution would probably be to relax the naming rules around utilities and ensure if the special characters are already escaped, they don't get escaped again