util: add a popoldest() method to lrucachedict This allows consumers to prune the oldest item from the cache. This could be useful for e.g. a consumer that wishes for the size of items tracked by the cache to remain under a high water mark. Differential Revision: https://phab.mercurial-scm.org/D4501

util: ability to change capacity when copying lrucachedict This will allow us to easily replace an lrucachedict with one with a higher or lower capacity as consumers deem necessary. IMO it is easier to just create a new cache instance than to muck with the capacity of an existing cache. Mutating an existing cache's capacity feels more prone to bugs. Differential Revision: https://phab.mercurial-scm.org/D4500

util: make capacity a public attribute on lrucachedict So others can query it. Useful for operations that may want to verify the cache has capacity for N items before it performs an operation that may cause cache eviction. Differential Revision: https://phab.mercurial-scm.org/D4499