[flagd] [FEATURE] Harden Hashing Consistency And Add Support For Non-string Attributes in Fractional Evaluation

[cupofcat]

Implement this ADR for the flagd provider.

[toddbaert]

Duplicated by: #360 and #359

[m-olko]

Hey, @toddbaert I don't think they are duplications of this issue. They are targeting nested operators and high-resolution bucketing, while ADR mentioned by @cupofcat is about supporting non-string attributes as a bucketing key. Could you reopen this issue and assign it to me? I'm working on this in C++ and can tackle Python implementation too.