Admin Performance: Jetpack Scan Menu Options and Availability Check

### Impacted plugin

Jetpack

### Steps to Reproduce

Go to /wp-admin

### A clear and concise description of what you expected to happen.

_No response_

### What actually happened

“Backups & Scans” would very occasionally appear in my Jetpack submenu in wp-admin, even without Backups or Scan active.

### Other information

My test site doesn’t have Jetpack Scan or Backup — I will have to test with these features another time, but my focus on this round was around base Jetpack.

However, I noticed that “Backups & Scans” would very occasionally appear in my Jetpack submenu in wp-admin.

After some digging, I found that it depends on a transient called jetpack_scan_state, [which only lives for up to 30 minutes](https://href.li/?https://github.com/Automattic/jetpack/blob/master/projects/plugins/jetpack/_inc/lib/class.core-rest-api-endpoints.php#L1715). When the transient isn’t present or has timed out, [the admin side-bar acts as though the user has Jetpack Scan enabled](https://href.li/?https://github.com/Automattic/jetpack/blob/master/projects/plugins/jetpack/modules/scan/class-admin-sidebar-link.php#L157). This adds both the menu item and a bunch of extra resources to the page. It then schedules a wp-cron job to refresh the transient on a subsequent page-load.

You can replicate this behavior by deleting the transient and loading any wp-admin page.

I recommend:

- Extend the life of the Jetpack Scan transient, and
- Look for ways to avoid loading Jetpack Scan resources for sites without the feature.

Internal reference: p1HpG7-evU-p2

### Operating System

_No response_

### OS Version

_No response_

### Browser

Chrome/Chromium

### Browser Version(s)

_No response_