Eagerly purge deleted items from internal LRU queues

[bitfaster]

When items are deleted, they remain in the internal queues until fully cycled out of cold. This is because the cycle/route methods do not inspect WasDeleted. Instead, purge them as items transition from queue to queue as part of cycle.

This change doesn't trigger double dispose/event due to the implementation of the Move method first attempting to remove the item from the dictionary:

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private int Move(I item, ItemDestination where, ItemRemovedReason removedReason)
        {
            item.WasAccessed = false;

            switch (where)
            {
                case ItemDestination.Warm:
                    this.warmQueue.Enqueue(item);
                    return Interlocked.Increment(ref this.counter.warm);
                case ItemDestination.Cold:
                    this.coldQueue.Enqueue(item);
                    return Interlocked.Increment(ref this.counter.cold);
                case ItemDestination.Remove:

                    var kvp = new KeyValuePair<K, I>(item.Key, item);

                    // when the item is already removed, skip event/metric counting
                    if (this.dictionary.TryRemove(kvp))
                    {
                        OnRemove(item.Key, item, removedReason);
                    }
                    break;
            }

            return 0;
        }

Scenarios covered:

• Item removed from hot during warmup
• Item removed from hot after warmup
• Item removed from warm during warmup
• Item removed from warm after warmp
• Item removed from cold after warmp
• Item removed then call TrimExpired
• Item removed then call Trim

Found two other bugs in Trim logic:

• TrimExpired missed the lock to make it thread-safe
• When trimmed item is in cold queue, we always trimmed an additional item from warm, which is incorrect.

[coveralls]

coverage: 99.169% (-0.06%) from 99.229%
when pulling 2f68804 on users/alexpeck/remremoved
into 01805a5 on main.