Update price rounding to be more accurate, show more decimals

[StephenHeaps]

Description:

We should handle price formatting more accurately by not restricting to 2 decimal places.

ref: https://bravesoftware.slack.com/archives/C04JJNFRPK7/p1706044166571059

We should do a manual pass on all price displays and align as appropriate.

[srirambv]

Verification passed on iPhone 13 with iOS 17.5.1 running 1.67 (100)

• Verified steps from brave/brave-core#23374
• Verified price/fiat display throughout wallet, in Portfolio, Asset Details, Transactions (fiat value + gas fiat value), Accounts
• Verified when Fiat/price values less than 1, shows value more accurately using 3 significant digits
• Verified when Fiat/price values less than 10 (>= 1), shows value with 3 digits after decimal
• Verified when remaining larger values (>= 10), shows value with 2 digits after the decimal matching existing behaviour