chore: move packages to packages/ directory, use npm deps instead of file deps

[anthonyting]

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Description

chore: move packages to packages/ directory, use npm deps instead of file deps.

This is the standard approach for npm workspaces:

• sdk-js-v3: https://github.com/aws/aws-sdk-js-v3
• npm docs: https://docs.npmjs.com/cli/v11/using-npm/workspaces
• powertools: https://github.com/aws-powertools/powertools-lambda-typescript

Also using npm links with * instead of file links. When publishing, we'll need to use npm links (and use an actual version instead of *)

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