chore(coinbase): transition to v3 Buy API

[Syn-McJ]

Coinbase v2 Buy APIs are being shutdown, so we need to switch to v3.

Issue being fixed or feature implemented

• Move the Coinbase feature out of the separate activity into the nav_home graph.
• Rename packages to align with other integrations.
• Replace v2/accounts with api/v3/brokerage/accounts calls.
• Replace v2/accounts/{account_id}/buys with api/v3/brokerage/orders calls.
• Rearrange Buy flow: no need to create and commit an order as the /orders endpoint executes the order immediately.
• Other refactoring to improve some unneeded/convoluted code.

Related PR's and Dependencies

Screenshots / Videos

How Has This Been Tested?

• QA (Mobile Team)

Checklist:

• I have performed a self-review of my own code and added comments where necessary
• I have added or updated relevant unit/integration/functional/e2e tests

[HashEngineering]

Excellent work.