SP-943 Python SDK should handle scientific notation

[bobbrodie]

Overview

As reported by DorskFR on #110, we can sometimes have values for paymentTotals.* and paymentSubtotals.* can come back as scientific notation, for example:

...
"paymentSubtotals": {
  "BTC": 1394587,
  "BCH": 200349400,
  "ETH": 298189000000000000,
  "GUSD": 86000,
  "PAX": 860000000000000000000,
  "BUSD": 860000000000000000000,
  "USDC": 860000000,
  "DOGE": 586597875600,
  "LTC": 1089539700,
  "MATIC": 1.321044547e+21,
  "USDC_m": 860000000,
  "USDT": 860410000,
  "USDT_m": 860410000,
  "PYUSD": 860000000,
  "USDCn_m": 860000000
}
...

Scientific notation values such as 1.321044547e+21 while uncommon are valid in JSON per ECMA-404:

A number is a sequence of decimal digits with no superfluous leading zero. It may have a preceding minus
sign (U+002D). It may have a fractional part prefixed by a decimal point (U+002E). It may have an exponent,
prefixed by e (U+0065) or E (U+0045) and optionally + (U+002B) or – (U+002D). The digits are the code
points U+0030 through U+0039.

The number 1.321044547e+21 is valid Python as well, however it is too large for an int, so we need to define these fields as a Decimal type from the decimal library.

Changes

• Import the decimal library
• Use the Decimal type instead of int

Notes

Testing shows that this is not required for 5.0.x as these were being defined as None.