Update CONTRIBUTING docs, remove unused scripts, cleanup `package.json`

[rygine]

in this PR:

• removed unused buf.sh script
• removed clean:proto command
• added .node-version for better compatibility with nodenv
• added bundler exports to files key in package.json
• updated contribution guide

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[github-actions[bot]]

:tada: This PR is included in version 11.3.2 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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