Don't track frozendicts whose contents can never be tracked by the GC

When a frozendict is created, we can check whether all of its keys and values are objects that can never be tracked by the GC. If so, the frozendict can never be part of a reference cycle, so it can be left untracked, like gh-140232 did for frozenset. Since frozendicts are immutable, checking once at creation time is enough.

I'm preparing a PR for this.

Linked PRs

• gh-155178

先查看链接的 PR gh-155178，然后跟踪 frozendict 的创建及其垃圾回收器跟踪行为。完成标准是：键和值永远不可能被 GC 跟踪的 frozendict 保持不被跟踪，而其他 frozendict 保持现有行为。