Add dynamic auth token updates

[zoedsoupe]

Problem

JS has setAuth(token) to update tokens without recreating client. Elixir requires new client instance.

Proposed Solution

# Option 1: Functional update
client = Supabase.Functions.update_auth(client, "new_token")

# Option 2: Per-request override
Supabase.Functions.invoke(client, "fn", auth: "new_token")

Benefits

• Token rotation support
• Better performance
• Feature parity with JS

JS Reference: functions-js/src/FunctionsClient.ts:56-62