Function activationKey cannot reliably support Ctrl+C on macOS

### Summary

I am trying to configure React Grab so either `Cmd+C` or `Ctrl+C` can trigger the copy/grab shortcut on macOS.

Using a function `activationKey` lets the keydown path recognize both shortcuts, but `Ctrl+C` still does not reliably activate/copy. It looks like the keyup/release path derives required modifiers from the platform default when `activationKey` is a function, so on macOS it still treats `Meta` as the required modifier even when the custom matcher matched `Ctrl+C`.

### Example configuration

```ts
import { getGlobalApi } from "react-grab";

const reactGrab = getGlobalApi();

reactGrab?.setOptions({
activationKey: (event) => {
const key = event.key.toLowerCase();
const isCopyKey = key === "c" || event.code === "KeyC";
return isCopyKey && (event.metaKey || event.ctrlKey) && !event.shiftKey && !event.altKey;
},
keyHoldDuration: 0,
});
```

### Expected behavior

When `activationKey` is a function and returns `true` for `Ctrl+C`, React Grab should use that matched shortcut consistently for the full hold/copy lifecycle.

In this case, both `Cmd+C` and `Ctrl+C` should be viable on macOS.

### Actual behavior

`Cmd+C` behaves as expected on macOS, but `Ctrl+C` does not reliably trigger/copy, even when `activationKey` returns `true` and `keyHoldDuration` is set to `0`.

### Source-level notes

From reading the current source:

- `packages/react-grab/src/utils/is-target-key-combination.ts` honors a function `activationKey` in the keydown path.
- `packages/react-grab/src/utils/parse-activation-key.ts` has `getModifiersFromActivationKey()`, but for a function activation key it returns platform defaults:
- macOS: `metaKey: true`
- non-macOS: `ctrlKey: true`
- `packages/react-grab/src/core/index.tsx` uses `getRequiredModifiers()` in the keyup path to compute `isReleasingModifier`.

That means a function matcher can say "this Ctrl+C keydown is valid", but the later release logic still appears to evaluate macOS `Meta` as the required modifier. For an OR-style shortcut like `Cmd+C` or `Ctrl+C`, there does not seem to be a way for the function matcher to also tell React Grab which modifier/key combination was actually matched.

There is also a `MIN_HOLD_FOR_ACTIVATION_AFTER_COPY_MS` gate in the keyup path, so setting `keyHoldDuration: 0` is not enough to make a normal Ctrl+C press work reliably.

### Why this matters

The string form can represent one shortcut such as `"ctrl+c"`, but it cannot represent an OR shortcut like "use `Cmd+C` or `Ctrl+C`". The function form is the natural API for that, but today it loses release/modifier semantics.

### Possible fixes

A few possible directions:

- Let `activationKey` accept an array of strings/functions, e.g. `["cmd+c", "ctrl+c"]`, so modifier metadata remains parseable.
- Add an optional way for function matchers to declare required modifiers.
- Track the shortcut/modifiers that actually matched on keydown and use that for keyup/release handling instead of falling back to platform defaults for function activation keys.

Related but not the same as #398, which is about copy behavior while the toolbar is minimized. This issue is specifically about function `activationKey` release semantics on macOS.