fix: change order of arguments in fee transfer's calldata

[MegaRedHand]

Closes #780

Description

We were passing the Uint256 arguments in the fee transfers in big-endian order (most significative first) when in Cairo a Uint256 assumes a little-endian order:

// Represents an integer in the range [0, 2^256).
struct Uint256 {
    // The low 128 bits of the value.
    low: felt,
    // The high 128 bits of the value.
    high: felt,
}

This caused us to try a transfer for the original fee amount times 2**128, which in practice means a failed transaction every time.

This wasn't caught in integration tests, because they all use a gas price of 0.

This PR fixes this issue, modifies tests to use a gas price of 1, and changes error handling, so these kinds of errors can be more easily debugged.

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.

[codecov-commenter]

Codecov Report

Merging #783 (96d88fa) into main (996bb68) will decrease coverage by 0.02%.
The diff coverage is 97.14%.

@@            Coverage Diff             @@
##             main     #783      +/-   ##
==========================================
- Coverage   92.47%   92.45%   -0.02%     
==========================================
  Files          51       51              
  Lines       12049    12050       +1     
==========================================
- Hits        11142    11141       -1     
- Misses        907      909       +2     

Impacted Files	Coverage Δ
src/transaction/declare.rs	98.75% <ø> (-0.15%)	⬇️
src/transaction/error.rs	100.00% <ø> (ø)
src/transaction/invoke_function.rs	99.19% <96.15%> (-0.12%)	⬇️
src/transaction/fee.rs	98.78% <100.00%> (+0.01%)	⬆️
src/utils.rs	94.31% <100.00%> (+0.03%)	⬆️