[v6] Inconsistent behaviour of dynamic IDs in JS/JSX macros

Nobody has claimed this yet.

### Description

While working on #2514 I became aware of a potential bug/discrepancy in how Lingui processes dynamic IDs between JS Macros and JSX Macros:

1. **JS Macros (`t({ id: dynId, message: "Welcome" })`)**:
Preserves the dynamic AST node `dynId` in the output because Babel processes object properties directly. The output retains `"id": dynId`.
2. **JSX Macros (`Hello`)**:
The dynamic attribute is lost. `maybeNodeValue()` inside `macroJsx.ts` evaluates non-static JSX attributes to `null`. It strips the attribute, completely drops `dynId`, and instead relies on the hash fallback identifier from the text.

I'm not sure what the expected behaviour is but figured I'd surface this in case it's a bug.

### Example test snapshot

```tsx
import { Trans } from "@lingui/react/macro";
const dynId = "dynamic";
Hello;

↓ ↓ ↓ ↓ ↓ ↓

import { Trans as _Trans } from "@lingui/react";
const dynId = "dynamic";
<_Trans
{
/*i18n*/
...{
id: "uzTaYi",
message: "Hello",
}
}
/>;
```

### Verifications

- [x] I've checked [the docs](https://lingui.dev) and this isn't covered there.
- [x] I've searched existing issues on [GitHub](https://github.com/lingui/js-lingui/issues).

### Macro Support

Babel with babel-macro-plugin

### Lingui Version

6.0.0-next.3

Read macroJsx.ts, starting with maybeNodeValue(), and compare the JSX macro behavior with the JS macro behavior described in the issue. Use the supplied JSX snapshot as the regression case; done means the expected handling of dynamic IDs is decided and both macro paths behave consistently.

Written by the indexing model from the issue text.