feat: add lock and unlock methods

[damnsamn]

Summary

• add lock() and unlock() methods for manually controlling Lenis lock state
• preserve the locked state across internal resets by decoupling manual lock override (forceLocked) from transient internal locking
• prevent native scrollbar interaction while locked
• add playground controls/debug output to verify the behavior

resolves #513

Reasoning for this feature is included in the linked issue

[arzafran]

closing this as part of a backlog cleanup, we're keeping the open PR queue to work the core team is actively driving. thanks for the contribution, if the feature is still needed we'll revisit it via an issue.

[damnsamn]

Fair enough @arzafran

For what it's worth, I'm still making use of the functionality this adds in our project via a patch file, so it's proving itself out there, at least. So I'd call this feature still needed - by me, at least