Moved cache in message_type serializer to ConcurrentHashMap

[jbaron]

Moved cache in message_type serializer to ConcurrentHashMap to avoid concurrent modification exceptions. ConcurrentHashMap seems a good fit due to low overhead when reading from the map (which is the main purpose of a cache).

Updated both MessageTypeSerializer and DetailsLevelSerializer.

[jbaron]

Test were running fine on my laptop, so not sure what went wrong in the TeamCity build. I cannot access details of what went wrong, since it requires a jetbrains email account.

[ileasile]

Thank you for PR! Please run Reformat.. run configuration, I think there's an issue with imports order. Also, run :check instead of :test, it also checks formatting and Readme consistency. And it's actually run on TC

[jbaron]

@ileasile thanks for fixing it, not sure what the logic behind "Imports must be ordered in lexicographic order" exactly implies. It is clearly not as simple as alphabetically ordered.

[ileasile]

Yes, it's some order that our formatter respects :)