Support for more String transformation actions #1324

I've been using Valibot for a project where I'm constantly converting between different naming conventions (API uses snake_case, frontend uses camelCase), and I noticed that while we have toLowerCase() and toUpperCase(), we're missing the more common case transformations.

What I need

I keep writing custom transforms to convert to/from snake-case, kebab-case, etc. But it would be much cleaner/nice to have built-in actions like so:

toCamelCase() - "hello_world" → "helloWorld"
toSnakeCase() - "helloWorld" → "hello_world"
toKebabCase() - "helloWorld" → "hello-world"
toPascalCase() - "hello_world" → "HelloWorld"

This comes up constantly when:

• Converting API responses (backend uses snake_case, frontend uses camelCase)
• Processing form inputs for URL slugs
• Normalising data between different systems

Right now I either write custom transforms or pull in libraries like lodash just for these functions.

Proposal implementation

I looked at how toLowerCase is implemented and it seems pretty straightforward to follow the same pattern. Would be happy to take a shot at implementing this if you think it fits with Valibot's direction.

The logic isn't too complex:

// rough idea for camelCase
const toCamelCase = (str: string) => 
  str.replace(/[-_\s]+(.)?/g, (_, char) => char ? char.toUpperCase() : '');

Possible performance considerations

If you're concerned about the use of regex for transformation here slowing things down, we could implement this using either character iteration or a split/join approach, using regex only when it's absolutely necessary.

What do you think? Happy to work on a PR if this sounds good!