schwab_equity_award_json parser can introduce rounding errors in share quantity

[m01]

The schwab_equity_award_json parser can introduce rounding errors when selling an integer number of shares, which can trigger asserts later.

The workaround in https://github.com/KapJI/capital-gains-calculator/blob/main/cgt_calc/parsers/schwab_equity_award_json.py#L232-L282 for dealing with missing decimal numbers after the decimal point in some early Schwab exports can introduce rounding errors in the quantity of shares being sold, which can later trigger asserts (e.g. the one that checks if you're selling more shares than you have).

The problematic line is https://github.com/KapJI/capital-gains-calculator/blob/main/cgt_calc/parsers/schwab_equity_award_json.py#L282.

I'll try to come up with a repro and will update this bug accordingly. (EDIT: done, see #575)

I think a simple fix is to check if you can reproduce the sale total $ number from the transaction using the per share price, quantity, fees and rounding.