fix!: use bun as package manager when bun.lock is found

[pieh]

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Summary

Fixes https://linear.app/netlify/issue/FRB-1544/bunlock-not-selecting-bun-bunlockb-works

This is a BREAKING CHANGE as it changes the shape of public API

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BEGIN_COMMIT_OVERRIDE
fix: use bun as package manager when bun.lock is found

BREAKING CHANGE: packageManager.lockFile field containing single name of lock file is removed from output and packageManager.lockFiles field with array of possible lock files is introduced
END_COMMIT_OVERRIDE

[mrstork]

We could potentially opt to support both fields for a short period of time while calling the old one deprecated (maybe raise a warning message in the logs?). That way we can understand the scope of affected systems before we look to drop the field.

[pieh]

There is limited number of things using @netlify/build-info directly, so I think we can skip on interim period - this package is not meant for public consumption per-se as it's quite Netlify specific, so I don't think it warrants extra effort to have a ~deprecation period. Instead maybe we just have a canary with this change that we adjust consumers of this package before we merge and publish this change so we can minimize "package upgrade downtime"

[pieh]

Published ~canary https://github.com/netlify/build/releases/tag/build-info-v8.0.0-pre-20250103.0.0 for testing (yikes with preid with double .0 there :D I definitely held https://github.com/netlify/build/blob/main/.github/workflows/pre-release.yml wrong hehe )