Refactor: Cache whole iso4217 table in Nim

[dlipicar]

Description

We're currently making several calls to status-go functions IsCurrencyFiat and GetFiatCurrencyMinorUnit, which simply perform a lookup on a static table. Fetch the whole table and keep it in memory on the Nim side instead.

• Add method to status-go for fetching the complete FiatSymbol -> DecimalPlaces Table.
• Retrieve that table and cache it in the Currency service during application startup (the table is static, it will only change with a new version of the iso4217 library, so we are able to do this only once for the lifetime of the application)
• Move functions isCurrencyFiat and getFiatDisplayDecimals from the utils to the service and make sure they use the cached table instead of calls to the backend.

[dlipicar]

Deprecated by https://github.com/status-im/status-desktop/pull/9547