Fix #8482, #8519: NFT loading improvement

[nuo-xu]

Summary of Changes

1. Wallet is only fetching junk NFTs from SimpleHash when an auto-discovery assets process is completed
2. Only display the skeleton loading when wallet is fetching junk NFTs
3. Caching NFTs balance and metadata

This pull request fixes #8482 #8519

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:

Opt-in auto-discovery from NFT tab

1. fresh install and set up a wallet has some NFTs
2. go to wallet/portfolio/NFTs, and opt-in auto-discovery from the pop-up
3. observe NFTs are being fetched as well as junk NFTs
4. Other functionalities in this view should still work

Opt-in auto-discovery from settings

1. fresh install and set up a wallet has some NFTs
2. go wallet settings, and opt-in auto-discovery
3. go to portfolio/NFTs
4. observe no pop-up will show up but NFTs are being fetched as well as junk NFTs
5. Other functionalities in this view should still work

Filter update

1. Continue from previous
2. Open filter in Portfolio/NFTs
3. turn on or off Network Logo and save
4. observe network icon will be shown or hidden respectfully with no loading state.

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).