/**
 * Deep equality with NaN-safety and cycle detection.
 *
 * - `NaN === NaN` is false in JavaScript, so the previous `Object.is`
 *   tail correctly handled that case but only at the leaf — a
 *   `[NaN, NaN]` pair compared element-by-element worked, but compound
 *   structures relied on the tail. The new shape preserves that.
 * - Circular references used to send isDeepEqual into infinite recursion
 *   (`a.self = a; isDeepEqual(a, a)` blew the stack). A WeakSet of
 *   already-visited objects breaks the cycle and treats two structurally
 *   identical cycles as equal.
 * - Dates, regular expressions, Maps and Sets are compared by what they
 *   HOLD. Only arrays and plain objects had branches, so everything else
 *   fell through to the `Object.is` tail — which for an object means
 *   reference identity. `isDeepEqual(new Date(0), new Date(0))` was
 *   therefore false, as were two equal `/a/g`s, two Maps with the same
 *   entries and two Sets with the same members. A Date nested anywhere
 *   inside a structure took the whole comparison down with it, which is
 *   how this stayed unnoticed: the common shapes are objects and arrays,
 *   and those worked. Typed arrays and ArrayBuffers compare by their bytes
 *   for the same reason.
 * - Errors and host objects (URL, Headers, Blob, …) are deliberately NOT
 *   handled and still compare by identity. Unlike the types above they have
 *   no single obvious structural identity - whether two Errors with the same
 *   message but different stacks are "equal" is a policy question, not a
 *   fact - and there is no end to the list. Guessing an answer silently is
 *   what made the cases above wrong.
 */
export declare function isDeepEqual(value1: unknown, value2: unknown, seen?: WeakMap<object, object>): boolean;