Cache token balances

[StephenHeaps]

Description:

We should cache token balances for each account in Core Data so user doesn't have to wait for full balances fetch for all assets to load

https://bravesoftware.slack.com/archives/C023VS4HJ6Q/p1676011945567489

In summary, balances in Portfolio (Assets) will be refreshed when

1. A wallet is created
2. A wallet is restored
3. When wallet is unlocked
4. A account is created or added
5. A network is added
6. An asset is added
7. An asset's visibility status is changed to be visible
8. A transaction is confirmed or error out or dropped

[srirambv]

Verification passed on iPhone 13 with iOS 17.4 running 1.64 (109)

• Verified steps from brave/brave-core#22029
• Verified on a clean wallet loads all tokens with 0 balance
• Verified closing wallet and reopening wallet without locking doesn't do a balance refetch
• Verified restoring wallet on a clean install loads wallet balance
• Verified closing wallet and reopening wallet without locking doesn't do a balance refetch
• Verified auto-discovery of NFT works as expected
• Verified adding a token with balance to visible asset automatically updates balance
• Verified adding/removing token from visible list updates balance
• Verified adding/removing custom network updates portfolio balance
• Verified submitting a transaction updates the token and portfolio balance
• Verified upgrading from older version with balance, there is no balance refetch everytime wallet is opened (dismiss without locking)