fix: Add missing js extension for json canonicalizer import

[aldigjo]

What issue is this PR fixing

fixes #1174

What is being changed

A clear description of what this PR brings.

Quality

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• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
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• I added unit tests.
• I added integration tests.
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Details

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[mirceanis]

This looks correct. Thanks for adding this.
The tests are failing for unrelated reasons