protected int sizeOf(@NonNull K key, @NonNull V value) {
        return 1;
    }
Returns the size of the entry for {@code key} and {@code value} in
user-defined units.  The default implementation returns 1 so that size
is the number of entries and max size is the maximum number of entries.

<p>An entry's size must not change while it is in the cache.
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/util/collection/LruCache.java