Fix #6982: Auto-complete adding known custom assets

[StephenHeaps]

Summary of Changes

• Fix logic for auto-complete only working for Ethereum addresses, so Solana mint addresses were not checked against known assets.
• Set network of autocompleted token
• Fetching token info is currently only supported on Ethereum Mainnet, however you can add a Ethereum Mainnet asset while on any network with multichain updates so we should no longer check the selected network is ethereum mainnet.

This pull request fixes #6982

Submitter Checklist:

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

Test Plan:

1. Enter a custom Solana asset (in our blockchain registry) contract address:
   • ex. USDC mint address: EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v
   • ex. Wrapped BAT (Portal) mint address: EPeUFDgHRxs9xxEPVaL6kfGQvCon7jmAWKVUHuux1Tpz
2. Verify details auto-complete, asset can be added
3. Add a custom Ethereum asset in our blockchain registry
   • ex. Wrapped BTC contract address: 0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599
4. Verify details auto-complete
5. Add a custom Ethereum asset not in our blockchain registry (requires network lookup)
   • ex. UNI contract address: 0x1f9840a85d5af5bf1d1762f925bdaddc4201f984
6. Verify details auto-complete

Encountered #6989 during development

Screenshots:

6982.mp4

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).