Point at Bevy main

[tychedelia]

Because we're doing some things that are slightly unusual, we may need to make some small changes upstream to support our patterns. For example, I just had to open bevyengine/bevy#22024.

Because we are committing our lockfile, depending on an unstable branch should be fine, we just need to make sure that everything builds when running cargo update to bring in a new Bevy version.

The downside here would be if we depend on third party Bevy ecosystem crates, for example bevy_vello. However, we're not there yet and in many cases it's possible just to patch the dependency assuming there aren't major breaking changes: https://doc.rust-lang.org/cargo/reference/overriding-dependencies.html#the-patch-section. Ecosystem crates also always appreciate a PR to bring them up to date. (:

But let's cross that bridge when we get there!