Allow bsn caching syntax for zero-argument function calls

[laundmo]

Objective

In #24367 the caching syntax using the : prefix was limited to only being allowed in front of scene functions without arguments. The way this check was implemented meant the following was not valid: :scene() even tho :scene is converted to scene() in the macro anyways. Theres an argument for disallowing () call syntax from the start, to make it obvious whats going on, but at least when working in the context of the Rust macro, a function name being converted to a function call seems unintuitive.

Solution

Change the check used to allow zero-argument :scene() calls as well as :scene auto-called functions.

Testing

• cargo test --lib bevy_scene
• cargo run --example feathers_gallery --features=bevy_feathers

[laundmo]

Needs-Design for the open question of whether we even want to allow this