Move futures.rs, ConditionalSend and BoxedFuture types to bevy_tasks

[mnmaita]

Objective

• Related to Remove or shrink bevy_utils #11478

Solution

• Moved futures.rs, ConditionalSend ConditionalSendFuture and BoxedFuture from bevy_utils to bevy_tasks.

Testing

• CI checks

Migration Guide

• Several modules were moved from bevy_utils into bevy_tasks:
  • Replace bevy_utils::futures imports with bevy_tasks::futures.
  • Replace bevy_utils::ConditionalSend with bevy_tasks::ConditionalSend.
  • Replace bevy_utils::ConditionalSendFuture with bevy_tasks::ConditionalSendFuture.
  • Replace bevy_utils::BoxedFuture with bevy_tasks::BoxedFuture.

[mnmaita]

Wondering if the added alloc feature is the proper way to do it or if there's a different way.

[bushrat011899]

Totally agree with this change, just need to remove the alloc feature from bevy_tasks since we can safely assume access to an allocator.

[bushrat011899]

Within bevy_tasks, alloc is mandatory, so this feature isn't required.

[bushrat011899]

It should be sufficient to just remove these cfg(...) attributes in order to remove the alloc feature. This will also need to be done in futures.rs.

[mnmaita]

Thanks for chiming in on this one, I was unsure what to do with it.

Removed the feature and the cfgs. There were no instances of this in futures.rs FWIW.