fix: minimize features activated with leptos_axum's default feature

[k9withabone]

Closes #1835. I had to edit a couple of examples' tokio features to get them to work. Unfortunately, I think this means that this a breaking change, per the cargo book.

• leptos_axum default feature:
  • remove tokio/full, axum/macros
  • add tokio/fs, tokio/sync
• example leptos-tailwind-axum:
  • enable tokio's rt-multi-thread and macros features
• example ssr_modes_axum:
  • enable tokio's rt-multi-thread and macros features

[gbj]

Yes, this makes it a breaking change, as it would require users to enable additional Tokio features in a patch release, in a similar way to the examples. Totally fine to queue this up for 0.6, whenever it comes, but seeing as I released 0.5 on Saturday that's unlikely to be any time soon. But thanks for the PR.

[k9withabone]

Do you want me to rebase this so that it can be merged?

[gbj]

Yes, please, that would be great!

[k9withabone]

Should be good to go now.

[gbj]

Thanks!

[k9withabone]

Looks like this didn't get merged into main when you merged #2158.

[gbj]

Thanks — I missed the fact that it had been retargeted from main to the 0.6 branch, and was merged into 0.6 after I'd merged 0.6 into main. I'm opening a new PR to just move that commit over to the main branch from the 0.6 branch; your branch should be safe to delete.