Bump MSRV to 1.65

[chklauser]

The primary motivation is the option to use let-else for the C-like error handling that low level system APIs usually require.

I created this as a separate PR because I didn't want these changes and discussion around it to hold #1107 hostage.

While there are a lot of opportunities to use let-else in windows/disk.rs I ultimately didn't change that many cases, because more often than not, the code would have had the form

let Ok(()) = SomeWindowsApi(..) else {
  return Vec::new();
}

The let-else syntax does have the slight advantage that it forces you to diverge/return in the else block. That means you can't accidentally forget to return and fall through the else block. But compared to

if SomeWindowsApi(..).is_err() {
  return Vec::new()
}

it just reads weird ☹️.

In the process, I did find another interesting trick: Error::from_win32() internally calls GetLastError without wrapping it in a result. For cases where we don't expect a 0 success case from GetLastError, that seems simpler.

[GuillaumeGomez]

Looks good to me, thanks for the improvements! The CI is failing because you forgot to run cargo fmt. Please fix it and then I merge.

[GuillaumeGomez]

Thanks a lot!