Fix holdout initialization for missing includedFlags/excludedFlags

CRITICAL FIX: Make includedFlags and excludedFlags optional parameters
in Holdout entity to match Swift SDK behavior and fix fullstack
compatibility suite failures.

Root Cause:
- Global holdouts in datafiles may omit includedFlags/excludedFlags fields
- Python SDK required these as mandatory parameters
- Missing fields caused TypeError during ProjectConfig initialization
- This caused config to return None, resulting in "SDK not configured" error
- Swift SDK handles missing fields by defaulting to empty arrays

Changes:
- Changed includedFlags and excludedFlags from required to Optional[list[str]]
- Set default value to None, which gets converted to [] in __init__
- Matches Swift SDK behavior for handling missing fields in datafile

Impact:
- Fixes fullstack compatibility suite decide_holdouts.feature tests
- Global holdouts can now be parsed from datafiles without these fields
- All 47 holdout unit tests passing
- Backward compatible with existing datafiles that include these fields

Aligned with Swift SDK implementation.

Author: muzahidul-opti

optimizely/entities.py

@@ -220,8 +220,8 @@ def __init__(
         variations: list[VariationDict],
         trafficAllocation: list[TrafficAllocation],
         audienceIds: list[str],
-        includedFlags: list[str],
-        excludedFlags: list[str],
+        includedFlags: Optional[list[str]] = None,
+        excludedFlags: Optional[list[str]] = None,
         audienceConditions: Optional[Sequence[str | list[str]]] = None,
         **kwargs: Any
     ):