Improve user experience after buying topup credits from billing page

[dsiguero]

Video:
https://github.com/user-attachments/assets/5d4cc8f8-6a56-4f4a-ac4d-d281aa196805

Options so far:

Blocks UI:

• Add "Your credits are being added. Be patient" as a message in the spinner screen. Simple, fast to implement.

Non-blocking:

• Show a banner at the top/bottom saying "Your credits are being added".
• Show a spinner where the credits number is, until the condition is met (credits from API > credits in LocalStorage)