Standardize ScopedFuture::new_untracked like untrack() and untrack_with_diagnostics()

[zakstucke]

• Changes the behaviour of ScopedFuture::new_untracked to not emit diagnostics, in line with subscriber::untrack
• Adds new ScopedFuture::new_untracked_with_diagnostics, to match subscriber::untrack_with_diagnostics
• Replaces the call in ArcAsyncDerived::new_with_manual_dependencies to use ScopedFuture::new_untracked_with_diagnostics, as this one we want diagnostics.
• The other usage of ScopedFuture::new_untracked is in Action usage, which is left unchanged, thereby disabling diagnostics, which are not needed in this context.
• Adds untrack to the sync part of Action s to disable diagnostics there too

In case there's some confusion about why this is useful:

Having these diagnostics in action calls does not provide any value, a user is acutely aware that an action is something manually "dispatched". By disabling the warning, thereby it no longer being an error to use e.g. .get() inside an action, logic and getters that might contain signals and also be used in the view!{}/Effects, can be extracted into reusable functions, and not produce confusing warnings when used from actions.

[gbj]

Sounds great! The explanation all makes sense to me. Couple small notes on debug-cfg'ing, otherwise I'm happy.

[zakstucke]

I've had to restructure to avoid breaking semver, so we should merge this PR now, and #4274 for 0.9.

Edit: hmm actually looking at the diff again, this might still theoretically break semver in the CI check, because the future type is different, but imo in practice it will not break any user code so will be fine. should be fine now

[gbj]

Ah! Yeah, fair enough. I'm fine with the new version. Thanks, Zak.