Request: new collection, AtomicCache

[twyatt]

Potential future optimization (not tested):

public class AtomicCacheMap<K, V> private constructor(
    private val atomicMap: AtomicMap<K, V>,
    val maxSize: Int,
) : Map<K, V> by atomicMap {
    public constructor(maxSize: Int) : this(atomicMapOf<K, V>(), maxSize)

    fun clear() {
        atomicMap.mutate { this.clear() }
    }

    fun remove(key: K): V? =
        atomicMap.snapshotAndMutate { remove(key) }.getValue(key)

    fun putAll(from: Map<out K, V>) {
        from.forEach {
            put(it.key, it.value)
        }
    }

    fun put(key: K, value: V): V? =
        atomicMap.mutateAndSnapshot {
            if (this.size >= maxSize) {
                val toRemove = keys.take(maxSize - size + 1)
                    .toSet()
                this.minusAssign(toRemove)
            }
            this.minusAssign(key)
            this[key] = value
        }.getValue(key)
    
    operator fun set(key: K, value: V): V? = put(key, value)
}

Originally posted by @QuantumRand in https://github.com/JuulLabs/conx-sdk/pull/1614#discussion_r1689271840

[cedrickcooke]

It's probably worth spending a bit more time on the data structure. The proposed cache evicts based on insertion order, but an LRU cache seems more generally useful.