[FEATURE] Implement multi-provider

[toddbaert]

The mutliprovider needs to be implemented in Python. Instead of being added to the contrib repo, these are now to be added directly into the SDK (similar to the in-memory providers).

See full spec here: https://openfeature.dev/specification/appendix-a/#multi-provider

See implementations in JS, Go.

[vikasrao23]

Hi! 👋

I've implemented the Multi-Provider in PR #566.

What's included

• MultiProvider class - wraps multiple providers into one
• FirstMatchStrategy - sequential evaluation (stops at first success)
• EvaluationStrategy protocol - for custom strategies
• Provider name uniqueness - auto-generates unique names when needed
• Parallel initialization - all providers init concurrently
• Comprehensive tests - all flag types, fallback behavior, error handling

Example

from openfeature import api
from openfeature.provider import MultiProvider, ProviderEntry

multi = MultiProvider([
    ProviderEntry(primary_provider, name="primary"),
    ProviderEntry(fallback_provider, name="fallback")
])

api.set_provider(multi)

The implementation follows the OpenFeature spec and uses the JS/Go implementations as references.

Future work (suggested for follow-ups)

• Status aggregation (tracking READY/ERROR/FATAL states)
• Event re-emission to SDK
• Additional evaluation strategies (parallel mode, custom aggregation)
• Fully async evaluation

Let me know if any adjustments are needed!