fix: require whitespace after @const tag

[jrmajor]

Currently, {@constfoo = 'bar'} is a valid declaration of foo.

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[changeset-bot]

🦋 Changeset detected

Latest commit: a0be1aa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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svelte	Patch

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[baseballyama]

Thank you!