feat!: fractional bucketing improvements

[toddbaert]

High-precision and nested fractional

This is a coordinated feature across flagd and all flagd providers.

• fractional now supports up to max-int32 total weight and 1/max-int32 resolution as described in the high-precision fractional bucketing ADR
• fractional now supports computed (nested JSONLogic) variants and weights as described in the fractional ADR
• Includes e2e tests from the flagd-testbed v3.1.0...v3.5.0 to validate consistent fractional bucketing across all provider implementations
• ⚠️ Pseudorandom hash assignments will change with this release due to changes in the hashing algorithm; update flagd and your providers to ensure fractional assignment is consistent across all workloads

Related PRs

Component	PR
flagd	open-feature/flagd#1909
java-sdk-contrib	open-feature/java-sdk-contrib#1740
js-sdk-contrib	open-feature/js-sdk-contrib#1501
python-sdk-contrib	open-feature/python-sdk-contrib#373
dotnet-sdk-contrib	open-feature/dotnet-sdk-contrib#622
flagd-schemas	open-feature/flagd-schemas#207

Warning
@toddbaert will coordinate the release across flagd and all providers. Do not merge without coordination.

[toddbaert]

NOTE: there's barely any changes here - just submodule and go.mod updates since all of this is handled in libs from flagd.

[gemini-code-assist]

Code Review

This pull request updates the flagd/core dependency to v0.15.0 and jsonlogic to v3.9.0, alongside several other dependency updates for the flagd provider and its E2E tests. It also updates the flagd-testbed subproject commit. The E2E test configurations for the file, in-process, and RPC providers were modified to exclude the @fractional-v1 and @operator-errors tags. I have no feedback to provide.