text: Title: Functions not working due invalid URL formatting
  Body: Hi all,
  
  Calling functions using supabase-py for me allways results in the following response: 
  
  `{'data': b'Function not found', 'error': None}`
  
  I believe this is due to the improper URL format in the `FunctionClient`:
  https://github.com/supabase-community/supabase-py/blob/5c752443277de0a4a8dfd7d0d113f0d177efc81f/supabase/client.py#LL74C64-L74C64
  
  Overwriting the `functions_url` in the following format seems to work for me: `"{}/rest/v1/rpc".format(url)`