SUMMARY
After and update in Fedora 38, this feature no longer works.
I tried downgrading all rust* + cargo* packages, the issue remained. After downgrading Kate, the feature worked again.
Version known working: 22.12.3
Version known not working: 23.04.0

STEPS TO REPRODUCE
1. Open and Rust project in Kate with LSP plugin active and rust-analyzer binary available
2. In the following code:
```
struct S {}
impl Drop for S
{
    <CURSOR HERE>
}
```
press Ctrl + Space to force autocompletion menu.
In Kate version 22.12.3, it would autofill this string `fn drop(&mut self) {`.
In Kate version 23.04.0, it would autofill this string `fn drop(..)`.

OBSERVED RESULT
Arguments and return types of implemented methods are missing.

EXPECTED RESULT
Arguments and return types of implemented methods should be autofilled.

SOFTWARE/OS VERSIONS
Linux: Fedora 38