feat!: use alien-signals for reactivity

[littensy]

Rewrite Charm using the alien-signals reactive algorithm.

Why?

Adopting alien-signals brings benefits and guarantees like predictable effect ordering, nested effect cleanup, and more efficient computed() memoization, all without a significant compromise to performance. Building Charm on this signal algorithm should improve Charm's overall efficiency and reliability.

What's New?

• signal(initialValue): create a state container with a separate getter and setter function
• effectScope(fn): cleans up a group of effects and subscriptions
• onCleanup(fn): runs fn once the current effect/scope reruns or gets disposed
• listen(selector, listener): similar to subscribe(), but runs once immediately
• untracked(fn): similar to peek(), but doesn't track effects created inside
• trigger(getter): manually triggers an update in one or more signals
• Optimized mapped() to cache values and avoid unnecessary updates
• Optimized computed() to use lazy evaluation instead of eager updates

Breaking Changes

• peek() was changed to untracked() for parity with other state managers
• Nested effects automatically dispose when the parent effect reruns or the scope is disposed
  • This applies to observe(), which wraps observer calls in an effect scope.
  • Subscriptions are automatically cleaned up since they are also effects, but the listener callback runs in untracked(), so inner effects created in the listener are not tracked.
  • Use untracked() or create a detached effect scope if you need to run code outside the parent effect's lifecycle.
• Effects and subscriptions created inside observe() now automatically dispose when the item is removed

Notes

• In Roblox Studio, the following flags will be enabled by default:
  • flags.strict: Formerly _G.__DEV__, this bans unsafe yielding and enables additional checks in Charm Sync.
  • flags.frozen: Deep-freeze all atom values to enforce immutable state updates.

Known Issues

There are a few known issues with our implementation of alien-signals that will be fixed in a future release:

• Inner effects clean up after the parent effect re-runs rather than before #60
• Signals and computeds can link to different nodes when called in the same effect scope #61