WIP upgrade to leptos-0.7

[stefanboere]

Changes:

• Changed Rc<RefCell<..>> to Arc<Mutex<..>> everywhere to get Sync + Send
• Added many Send + Sync constraints
• Removed default_options from QueryOptions since not supported in Resource any more
• Switched to serde_json and serde over miniserde because leptos has a dependency on serde_json already anyway
• Undo async trait removal in 'WIP upgrade to leptos-0.7'; It is needed to use this type as trait objects
• Removed gloo_timers::future::sleep and used futures::future::pending instead as the future returned by gloo_timers::future::sleep is not Sync

Open issues:

• start-csr is still todo, but running into Send/Sync issues with JsFuture
• ResourceOption::Local option is still todo, don't know how
• Bug: The double use of Post 2 only loads the first post from browser cache, don't know why or how to fix
• 3 tests are still failing or are flakey, don't know why or how to fix
• The IndexedDb feature cannot be used due to Sync/Send constraints, don't know how to fix

Solved but not sure if solved correctly

• How the initial query fetch is done now, and how sleep is changed to something with signals, see commit cc04a8f
• How this should be converted to 0.7

if resource.loading().get_untracked()
     && !HydrationCtx::is_hydrating()
     && query.with_state(|state| matches!(state, QueryState::Created))
{
    query.execute()
}

Any help on these open points would be appreciated :).

[stefanboere]

I tried to do as much as possible, but running into a few difficult parts where I don't really know how to proceed. See the comments above. So for now I'll stop working on this. And I don't expect to be able to finish this in the future. But I'll leave this PR open so hopefully someone else can give it a try also :).

What works:

• Leptos_query compiles and base functionality seems to work as long as you use ssr and hydrate.
• start-axum works mostly
• leptos-query-axum-workspace works mostly
• localstorage feature kind of works

What doesn't work (see also comment above)

• csr
• Indexed_db feature
• ResourceOption::Local