Fixes #8472.

Description of the problem being solved:

Skills that combine both weapon's damage into one hit when dual wielding (Cleave, Dual Strike, Viper Strike, Whirling Blades) would report negative impale DPS under certain conditions like low impale chance or high enemy impale physical damage reduction.
Calculations are now done separately for each hand and then combined instead of averaging the impale base and modifier. This also fixes incorrect calculations in cases where one hand deals significantly more damage than the other (e.g. Dual Strike of Ambidexterity).

Steps taken to verify a working solution:

• doing the math manually
• new unit test added for simultaneous attack impale

Link to a build that showcases this PR:

https://poe.ninja/builds/phrecia/character/Expertas%234276/ExpertInTheBin?type=exp&i=5&search=skills%3DDual%2BStrike%2Bof%2BAmbidexterity

Before screenshot:

Negative impale dps:

After screenshot:

Non-negative impale dps:

Before/After of same POB with 100% impale chance (to show corrected calculations)