chore: cache flags, distinct id and anon id in memory to avoid file IO every time

[marandaneto]

💡 Motivation and Context

Closes #176
Only read the value from the storage if it's not in memory yet.
Setters always overwrite the value in the storage and memory.
Storage only will be accessed the very first time unless the value changes async (eg flags), then the memory value is also updated.
This should reduce the main thread warnings.
All values are read and updated using lockers already.

💚 How did you test it?

unit tests already exist and they are all green

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.