Pybit

- Enabled WebSocket `fetch()` to handle multiple position sides from linear perp symbols
- Fixed `fetch()` for private spot WebSocket
- Supported `endpoint` argument for `my_position()`, allowing the user to call this method without supplying a symbol
- `symbol` is not a required parameter for these endpoints, but pybit typically relies on it for deciding which endpoint to call
- See below release candidates for details.

Modified
- Alter the spot endpoint paths used for `get_active_order()` and `query_active_order()`

Modified
- Fixed failure to load subscriptions when provided in as JSON strings

Modified
- Fixed the spot auth WebSocket to ensure subscriptions are not required

Modified
- Fixed methods like `query_symbol()` (which have no API parameters) not working following the spot update

Added
- Implemented the Spot API in `HTTP`
- Implemented the Account Asset API in `HTTP`
- Implemented the Spot WebSocket in `WebSocket`