Consider TTL in constructor options / `.set`

[shhac]

Other than remembering commonly used invocations, another big use case for a cache is knowing when an item is time-stale.

Currently doing this with a Map or Set is possible by wrapping it manually, but having it wrapped outside has drawbacks that inclusion here could tackle

• The different policy types can first clear an expired entry when size limits are reached, meaning living data may persist longer
• Time checking can be implemented closer to the metal

ttl would default to never expires when not provided, and could be provided either at the level of the whole map/set as an option at construction time, or by adding an additional parameter to the .set method

const m = new Foo();
m.set('key', 'value', msToLive);
// or
m.set('key', 'value', { ttl: msToLive });