[FLI-1270] Create IOS/Android shared libs

Package engine for ios/android so we can start supporting mobile SDKs

_Originally posted by @markphelps in https://github.com/flipt-io/flipt-client-sdks/pull/351#discussion_r1747424310_
            

<sub>[FLI-1270](https://linear.app/flipt/issue/FLI-1270/create-iosandroid-shared-libs)</sub>