fix: avoid poisoning global scope

[Ayc0]

• Add a test if possible
  I didn't add any automated test, but I checked that after running pnpm build, there was no mention of Window in the index.d.ts file:
  
  I didn't add any test because:
  • this test would require to be ran after pnpm build
  • if we wanted to write to test to ensure that we aren't poisoning the global scope, we need to do something like "is Response, or Window, etc., in the generated code?" But Response is used so we cannot use that, and other may be used in the future. So I don't know which test we could write that could be future proof for this.
• Format all commit messages with Conventional Commits
• This PR fixes Global fetch type is getting modified by shiki #454

I couldn't use just declare var fetch and others, because we need to add to the global scope Window and others as they are used by shiki's node_modules (and so when running tests locally, we need them, see https://github.com/shikijs/shiki/actions/runs/4572982584/jobs/8072860830).

So I moved those to a global.d.ts so that they'd be present in the project, but not in the built code.

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[orta]

Yeah, I think this should do it 👍🏻

[orta]

Nice work!

[Ayc0]

Thanks!