Add `allow_client_traits_in_evaluation` to environment schema

Add a new `bool` field `allow_client_traits_in_evaluation` (default `True`) to the environment schema in `flagsmith-common`. This field controls whether client-sent traits are used for segment evaluation, separately from `allow_client_traits` which controls trait persistence.

The default of `True` preserves backwards compatibility — existing environments with `allow_client_traits=False` will continue using client-sent traits for evaluation until explicitly opted out.

Release a new `flagsmith-common` version with this change.