chore(extensions): fix type errors

[skirtles-code]

These 4 files currently report TS errors.

TS is unaware of how these files are being built, so it incorrectly believes that all the code will run in a global scope, leading to collisions between the files. For example, both devtools-background.ts files have a variable called created, which TS is treating as global and reports an error due to the duplicate declaration.

There are various ways to fix this, but I've just added export {} to each file, which tells TS to treat them as ES modules.

This doesn't impact how tsdown builds the files. The built files in dist are unchanged.

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commit: 87c20b7