Add apple keychain support

[BitPhinix]

I vibe-coded this entire thing but it's rather simple and works well

[theoephraim]

First off - thanks for the PR! :)

You sir, are in for a real treat. We have native keychain support baked into varlock core about to be released, and it's WAY better than deferring to the security cli :)

Theres a native swift binary that will be packaged with the npm module. It adds biometric fingerprint unlock, pinned to the current terminal session. Use ITEM=keychain(prompt) and you get a native mac popup to select an item, or add a new one. Automatically sets an ACL rule to limit access to said binary. Gets replaced in the file to to ITEM=keychain(some/id) and from then on resolves it normally (gated behind fingerprint).

Also we have a new varlock() resolver which uses secure enclave (behind fingerprint unlock) as an encryption key, but stores the encrypted value in the file, so no keychain involved.

You can install with the preview package available in this PR. Use https://pkg.pr.new/varlock@567 instead of a version number for varlock in your package.json. Would love to have some more feedback before it's released!

[BitPhinix]

Oh amazing, thanks for your hard work!