feat: add @discordjs/util (#8591)

* feat: add @discordjs/util

* fix: builders test

* refactor: make rest use lazy for ESM import

* chore: make requested changes

* Apply suggestions from code review

Co-authored-by: Parbez <imranbarbhuiya.fsd@gmail.com>
Co-authored-by: A. Román <kyradiscord@gmail.com>

* chore: make requested changes and add tests

* chore: regen lockfile

* test: add type tests

* chore: push missing files

* chore: make requested changes

* chore: update CI stuff

* chore: fix lockfile

* chore: make requested changes

Co-authored-by: Parbez <imranbarbhuiya.fsd@gmail.com>
Co-authored-by: A. Román <kyradiscord@gmail.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/util/src/Equatable.ts

@@ -0,0 +1,21 @@
+/**
+ * Represents a structure that can be checked against another
+ * given structure for equality
+ *
+ * @typeParam T - The type of object to compare the current object to
+ */
+export interface Equatable<T> {
+	/**
+	 * Whether or not this is equal to another structure
+	 */
+	equals(other: T): boolean;
+}
+
+/**
+ * Indicates if an object is equatable or not.
+ *
+ * @param maybeEquatable - The object to check against
+ */
+export function isEquatable(maybeEquatable: unknown): maybeEquatable is Equatable<unknown> {
+	return maybeEquatable !== null && typeof maybeEquatable === 'object' && 'equals' in maybeEquatable;
+}