Make tail leak repair time configurable

At Etsy we've been hit by the LRU tail refcount leak a bunch of times. We're currently using official 1.4.13.

The 3 hour default is a bit too long, we'd prefer to reduce it to something more manageable like 30s. With 30k req/sec once we hit the issue, over 20% of set requests start failing with the OOM error and stay that way until the 3 hours are up.