POS buggy with disabled fiat currency

[myxmaster]

Describe the bug

1. Enable fiat currency and create a POS order. Then go to Settings, diable fiat currency and create another POS order -> POS order view still displays fiat values (probably cached rates?). => We need proper reloading of fiat settings for this case.
2. After disabling fiat currency, kill the app and restart. Create another POS order -> It will display $N/A for Conversion rate which makes sense, but Total (Fiat) is $NaN (should be $N/A) and Total (Bitcoin) is NaN sats, but that sum should be calculated.

In general I think we should think about checking if fiat is enabled when POS is used ("Open" tab and creating an order, something else?) and if fiat is not enabled, display a modal with options to enable it or leave POS view.

Reproduce

...

ZEUS version

v0.9.5

Node interface

Multiple (specified in comments)

Network

Clearnet

Device

Pixel 7 Pro emulator

Device operating system

Android 14

Log output

No response

[myxmaster]

Maybe related to #2004