Olivero's secondary menus inoperable when authenticated & BigPipe present

I tested this on a fresh install of Drupal 11.3. Where previously it would show just the context menu but not the dropdown for nested items in the main navigation on hover, with the patch applied the menu works as expected even when logged in as an admin.

I was curious about why HTMX would make a difference, if the issue was that Olivero did not use behaviors, so I did some investigation with these steps:

1. Install core with standard
2. Go to /node/add/article
3. Full in a title, open the menu settings, check Provide a link, set the Parent link to Home, save
4. Observe hover behavior of Home link
5. Observe behavior of Home link after reload

On 11.2.x, the hover behavior of the home link on the first cold page load does not work as expected. It does work subsequently on reloads. This does confirm it's Big Pipe related, but 11.2.x does not use HTMX for Big Pipe.

I also tested against 11.1.x, and the hover behavior of the home link on the first cold page load does work as expected. If anything, either the issue was introduced between 11.1.x and 11.2.x (not going to do a git bisect now) or it was a race condition.

Based on #8, pretty sure it was #3437499: Use placeholdering for more blocks - before that issue, the main menu would be rendered with the main content, after that issue, on cache misses, it's rendered via big pipe, on cache hits, as part of the main content again (due to another change that landed in 11.2).

Reviewed the patch and made the following improvements:

1. Renamed init(el) parameter to init(navElement) to avoid variable shadowing with the el used inside the forEach callbacks
2. Added documentation to the init() function
3. Wrapped the document-level keyup and touchstart event listeners with once() to prevent duplicate handlers when the behavior is attached to multiple elements

Tested updated MR locally with same steps per #8 and still works as expected.

Thank you for the review @godotislate! Committed 🚀