Fix possibility of double initialization

[nickbabcock]

If, for whatever reason, someone had code that looked liked:

const [jomini1, jomini2] = Promise.all([
    Jomini.initialize(),
    Jomini.initialize()
]);

Previously the Wasm would be compiled twice. The fix is to detect if there is compilation in progress.

[github-actions[bot]]

Size Change: +4 B (0%)

Total Size: 95 kB

Filename	Size	Change
dist/es/index.js	95 kB	+4 B (0%)

_{compressed-size-action}