[Feature request]: Add pull token approach to Realtime

[grdsdev]

Feature request

To better align realtime with other libs (they all use a pull approach), let's:

• add an accessToken closure to the realtime client initialization;
• make SupabaseClient inject a method for pulling the access token from Auth.

Reference PR: supabase/supabase-swift#615

[arun-h]

Hello @grdsdev , I’d like to work on this issue

My approach is:
-Add an optional get_access_token: Callable[[], str] parameter when initializing the realtime client.
-Update the realtime client so it calls this function whenever it needs a token.
-Update Supabaseclient to inject a default method that fetches the current access token from auth.get_session().

This will mirror the approach taken in supabase/supabase-swift#615

Please let me know if you’d like any adjustments before I open a PR