More generic accounts purge functions (#14595)

Co-authored-by: Carl Lin <carl@solana.com>

runtime/src/contains.rs

@@ -0,0 +1,49 @@
+use std::{
+    borrow::Borrow,
+    cmp::Eq,
+    collections::{HashMap, HashSet},
+    hash::Hash,
+};
+
+pub trait Contains<'a, T: Eq + Hash> {
+    type Item: Borrow<T>;
+    type Iter: Iterator<Item = Self::Item>;
+    fn contains(&self, key: &T) -> bool;
+    fn contains_iter(&'a self) -> Self::Iter;
+}
+
+impl<'a, T: 'a + Eq + Hash, U: 'a> Contains<'a, T> for HashMap<T, U> {
+    type Item = &'a T;
+    type Iter = std::collections::hash_map::Keys<'a, T, U>;
+
+    fn contains(&self, key: &T) -> bool {
+        <HashMap<T, U>>::contains_key(self, key)
+    }
+    fn contains_iter(&'a self) -> Self::Iter {
+        self.keys()
+    }
+}
+
+impl<'a, T: 'a + Eq + Hash> Contains<'a, T> for HashSet<T> {
+    type Item = &'a T;
+    type Iter = std::collections::hash_set::Iter<'a, T>;
+
+    fn contains(&self, key: &T) -> bool {
+        <HashSet<T>>::contains(self, key)
+    }
+    fn contains_iter(&'a self) -> Self::Iter {
+        self.iter()
+    }
+}
+
+impl<'a, T: 'a + Eq + Hash + Copy> Contains<'a, T> for T {
+    type Item = &'a T;
+    type Iter = std::iter::Once<&'a T>;
+
+    fn contains(&self, key: &T) -> bool {
+        key == self
+    }
+    fn contains_iter(&'a self) -> Self::Iter {
+        std::iter::once(self)
+    }
+}