Show warning if @CacheKey is not present for custom serializer/deserializer

[ingver]

Hello!

I ran into a problem today, when my production build was throwing misterious errors like t.map is not a function. Spent some hours to localize an issue, then figured out that the reason was deserializers caching strategy, which doesn't work after minification. I've done some research and have read #2. @CacheKey was the solution. I consider it strange, that the problem isn't mentioned in the documentation.

Thus, I wanted to suggest an improvement. The library could warn about missing @CacheKey decorator, so developer would not occasionally shoot himself in the foot on production.

[Fattouh92]

I ran into the same problem today, was also fixed by @CacheKey. If there is only one custom deserialiser then no need for warning otherwise the need arises. I guess documentation should also be updated to show how to implement custom deserialisers and state that @CacheKey should be used