fix: allow false as a flag value

This commit updates Flag#from_api to support `false` as a valid value.

Previously, `false` values for `:feature_state_value` would would fall through
the `||` branch and end up using the value from `:value`, which in most (all?)
cases seems to be `nil`.

The previous behavior made it impossible to distinguish between the following
two cases:

- an enabled flag that has never had its value set
  (and should therefore be treated as `true`)

- an enabled flag that is explicitly set to `false`
  (and should therefore be treated as `false`)

With the change in this commit, the first case will be `nil`, and the second
case would be `false`. The `:value` key will now only be consulted when there
is no `:feature_state_value` key present in the JSON flag data.

Author: bdchauvette

lib/flagsmith/sdk/models/flags.rb

@@ -71,7 +71,7 @@ def from_feature_state_model(feature_state_model, identity_id)
         def from_api(json_flag_data)
           new(
             enabled: json_flag_data[:enabled],
-            value: json_flag_data[:feature_state_value] || json_flag_data[:value],
+            value: json_flag_data.fetch(:feature_state_value) { json_flag_data[:value] },
             feature_name: json_flag_data.dig(:feature, :name),
             feature_id: json_flag_data.dig(:feature, :id)
           )