The serialization extension assumes that currentsize is always measured by the number of items in the LRU.

If we use another by function to measure size, then we error trying to serialize (which is good because it looks like deserialize depends on this assumption).

using LRUCache
using Serialization

lru = LRU{String,Vector{UInt8}}(; maxsize = 1024, by = sizeof)
lru["asdf"] = rand(UInt8, 512)

# not the same
@assert lru.currentsize == 512
@assert length(lru) == 1

serialize(IOBuffer(), lru)
# ERROR: AssertionError: lru.currentsize == length(lru)

Would a PR contribution be welcome to help here?