Document safety expectations, or the lack thereof

I noticed that the instances for `Map`, `Set`, `IntMap`, and `IntSet` are "unsafe" in the sense that they will happily build structures that don't obey the expected invariants if they are presented with improperly ordered input. Is this acceptable behavior (i.e., is `get` only supposed to be used with trusted input)? Or should the invocations of `fromDistinctAscList` be replaced with `fromList`?

审查 Map、Set、IntMap 和 IntSet 实例，以及 issue 中提到的 fromDistinctAscList 调用。确定 get 是否用于受信任的输入，并记录安全性预期；或者，如果应替换这些构造函数，则确定所需的行为；完成工作需要项目作出明确决定。

由索引模型根据 Issue 内容生成。