fix: update cn function type and import cx from tailwind-variants/lite

[jrgarciadev]

• Change the type of cn function to allow callable string representation.
• Update import statement in MIGRATION-V3.md to use cx instead of cnBase.

Description

Fix this issue:

Type '(config?: TWMConfig | undefined) => CnReturn' is not assignable to type 'string'.

  // before
  <div className={cn("flex items-center justify-center gap-2", className)()}>

// after
  <div className={cn("flex items-center justify-center gap-2", className)}>

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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