Fix #8649: Improve Performance of Select Token to Send

[StephenHeaps]

Summary of Changes

• Tricky to reproduce the UI lock up, but more accounts and/or tokens with balance the more likely it could occur. 2 hopeful fixes applied to improve performance:
  1. SelectAccountTokenStore would build all account sections with all tokens, and use a computed property to filter out networks (from network filters) and tokens without balance. This would be expensive on the UI, so now the models are built once when network filters change, query changes, or user taps Show/Hide Zero Balances button. These models are built off the main thread using an async function for a bit extra perf with large accounts/token lists.
  2. We were fetching balances for each account sequentially (token for account were fetch concurrently). Now each account is fetched concurrently too, and off the main thread.

This pull request fixes #8649

Submitter Checklist:

• [x] Unit Tests are updated to cover new or changed functionality
• [x] User-facing strings use NSLocalizableString()
• [x] New or updated UI has been tested across:
  • [x] Light & dark mode
  • [x] Different size classes (iPhone, landscape, iPad)
  • [x] Different dynamic type sizes

Test Plan:

Unfortunately I did not find consistent reproduce steps for the UI lockup, so hard to verify the lockup but we should test view is still working as before (use a wallet with lots of accounts and tokens with balance):

1. Test opening send and verify Select a Token to Send is still working as expected.
2. Test networks filter & queries still working as expected.
3. Test 'Show Zero Balance' button still appears when no tokens are visible (new wallet, or filter to a network without balance on current wallet)

Screenshots:

Reviewer Checklist:

• [ ] Issues include necessary QA labels:
  • QA/(Yes|No)
  • bug / enhancement
• [ ] Necessary security reviews have taken place.
• [ ] Adequate unit test coverage exists to prevent regressions.
• [ ] Adequate test plan exists for QA to validate (if applicable).
• [ ] Issue and pull request is assigned to a milestone (should happen at merge time).

[github-actions[bot]]

[puLL-Merge] - brave/brave-ios@8654

Description

This pull request makes several changes to the SendTokenView.swift, SelectAccountTokenView.swift, SelectAccountTokenStore.swift, RpcServiceExtensions.swift, and SelectAccountTokenStoreTests.swift files. The changes include updates to the way token stores are selected and updated, improvements to fetching account and asset information, modifications to the handling of balances, and changes related to network filtering.

Changes

### Changes - `SendTokenView.swift`: Updates the way token stores are selected and updated. - `SelectAccountTokenView.swift`: Implements changes related to the fetching of account and asset information, as well as modifications to the handling of balances. - `SelectAccountTokenStore.swift`: Introduces various updates to the way token stores are selected and updated, and includes changes related to network filtering and the way balances are handled. - `RpcServiceExtensions.swift`: Adds a new method for fetching balances for tokens. - `SelectAccountTokenStoreTests.swift`: Includes corresponding tests for the changes made in the `SelectAccountTokenStore` functionalities.

Security Hotspots

1. There are no apparent security hotspots in the changes made.