Added defensive copy mechanism

[therealryan]

It can be really bad if mutable fields are added to messages - if those values can get updated independently of the message you're left trying to find out why your message has changed when nothing is touching the message itself. It's a painful problem to debug.

Hence the message types are quite strict about what value types can be added - by default they only accept types that we know are immutable.
I've recently butted up against this limitation:

• I wanted to add java.util.UUID values (the type is immutable)
• I wanted to add java.sql.Timestamp values (this type is mutable, but it would be really convenient to use it directly)

This change:

• Adds UUID to the set of immutable types
• Adds a new mechanism for allowing mutable types as values: you can register a defensive copy function against a type. That function is used when the value is added to the message (we make a copy and store that instead) and when values are accessed from the message (we return a copy of the value that is held by the message)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

100.0% Coverage
0.0% Duplication