feat: support spaces before cut comments

[sapphi-red]

Currently twoslash requires the cut comment to be at the beginning of the line.
If I wanted to cut out the type comment for a variable in a function, I have to write it like below.

function foo() {
  const x = "123"
// ---cut-start---
  /** @type {"345"} */
// ---cut-end---
  const b = "345"
}

But if that project uses prettier, it will be formatted and the comments will have a space before the // like below.

function foo() {
  const x = "123"
  // ---cut-start---
  /** @type {"345"} */
  // ---cut-end---
  const b = "345"
}

So I'll have to disable prettier for this part of the code (https://github.com/vitejs/vite/blob/48a2bbb9994f9cd67e3d7455a57f6579f64e784d/docs/config/build-options.md?plain=1#L51-L66).

This PR allows the cut comment to have space characters before.

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[sapphi-red]

export const reCutBefore =/^[\t\v\f\uFEFF\p{Zs}]*\/\/\s?---cut(-before)?---\r?\n/mgu

Accurately, the regex needs to be like this to include other characters that are treated as white space. https://developer.mozilla.org/en-US/docs/Glossary/Whitespace#in_javascript
But I guess the u flag has a perf impact and people won't use those characters.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.25%. Comparing base (249c9d7) to head (7a53d31).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #33   +/-   ##
=======================================
  Coverage   95.25%   95.25%           
=======================================
  Files          16       16           
  Lines        1982     1982           
  Branches      347      347           
=======================================
  Hits         1888     1888           
  Misses         94       94           

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