move core result into core utils

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/result/not_found.rs

@@ -1,12 +0,0 @@
-use super::Result;
-use crate::Error;
-
-pub trait NotFound<T> {
-	#[must_use]
-	fn is_not_found(&self) -> bool;
-}
-
-impl<T> NotFound<T> for Result<T, Error> {
-	#[inline]
-	fn is_not_found(&self) -> bool { self.as_ref().is_err_and(Error::is_not_found) }
-}