When polling server for changes manually, dev tools doesn't have/use the latest cache-bust value

[alexcottner]

When polling remote-settings server for changes manually, remote-settings dev tools can retrieve a stale cached value. This will cause the server timestamp to appear older than the local timestamp (if the local cache has already been updated).

As a fix, we could use a random cache-bust parameter so the dev tools always bypasses the cache.

[leplatrem]

We already use a random cache bust when user click on Sync:

remote-settings-devtools/extension/experiments/remotesettings/api.js

Line 109 in b1c70c8

expectedTimestamp: randomCacheBust,

And we already use a random cache bust when we execute RemoteSettings.inspect() since Firefox 118 https://bugzilla.mozilla.org/show_bug.cgi?id=1809884

https://searchfox.org/mozilla-central/rev/e46f8390a67732e08d6c04729f27631edec98aeb/services/settings/remote-settings.sys.mjs#610-616

[alexcottner]

I think it's two small issues:

1. When we call sync for an individual collection, it doesn't use the cache bust value. This seems easy to fix.
2. After we click the main sync button, we call Services.obs.notifyObservers(null, "remotesettings-state-changed"); which causes a second API call with _expected=0 which can return a cached response.