millisat precision

[accumulator]

support millisat precision throughout the codebase.

• kwarged backend wallet funcs so it is clear whether sats or millisats as ints are passed
• lnurl now native millisats
• Decimal is used on the GUI side where it's easier to assume sats are the base unit
  • avoids having to check sat and msat fields/parameters
  • can check easily if amount has millisat precision where not allowed
  • extra millisat precision is carried transparently for eventual passing to backend
• QML QEAmount is now synced between sats and millisats, simplifying assumptions and reducing if-else checks

should fix #6253, #10412

[SomberNight]

The Claude CI task AFAICT correctly flagged (a preexisting) overflow issue here: property int is a signed 32-bit int, which is too small for this usecase.
The max value is around 21 BTC with sat units, and around 21 mBTC with msat units.

[accumulator]

Yes this is a long-standing issue, hence the use of QEAmount. A short summary of the issues:

• integers in javascript context have a max range of +/- 2^54-1, which allows 21M BTC expressed in sats, but not in msats.
• QML int properties have a max range of +/- 2^31-1, which only allows 21 BTC expressed in sats, 21 mBTC expressed in msats (like you already indicated above)
• int parameters declared in the pyqtProperty and pyqtSlot decorators have a max range of 2^31-1, although this is somewhat alleviated in the QML->Python direction by using q(u)int64. Returning a q(u)int64 does not work around the int limitation if I remember correctly (I think this was observed using Qt5, and when initially porting to Qt6)

In most of the QML code, QEAmount is already used for storing and passing around BTC values. The only exception is where amounts are compared (e.g. invoice amount < available balance etc) , so the <, >, <=, >= and != operators, and where these operators are implied, like Math.min() and Math.max()

I'm adding patches to add these operators as pyqtSlots so the operators are executed in python context. Possible caveat is that pyqtSlot calls might not be re-evaluated when used in a QML property binding.