[FEATURE] High-resolution fractional bucketing in flagd provider

[toddbaert]

Sub-issue of open-feature/flagd#1903. See the parent issue and ADR for full details.

Replace the current 100-bucket float-based fractional bucketing with integer arithmetic using MaxInt32 (2,147,483,647) as the max weight sum:

bucket = (uint64(hashValue) * uint64(totalWeight)) >> 32

Weights must be integers and sum to at most MaxInt32. Python: arbitrary precision integers handle this natively, use >> 32 for shift.

This is a behavioral breaking change (bucket assignments will shift), but the API surface is unchanged.

⚠️ Dependency: complete the nested fractional evaluation feature first: #359

@toddbaert will coordinate the release across providers.

[leakonvalinka]

I'll start working on this!

[toddbaert]

@leakonvalinka You may want to consider doing this at the same time, or at take it too, or you may have some tough git conflicts.

[leakonvalinka]

okay i see, thanks for the heads-up, i guess it makes the most sense to do both at the same time then.