Is killing by poison considered intentional killing or semi-intentional, and what are the jurists' opinions on that, especially the Hanafis?

The Hanafī school does not mandate Qisas (retaliation in kind) for killing by poison whatsoever. Rather, they sometimes consider it subject to Diyah (blood money) in cases of شبه العمد (akin to involuntary manslaughter), or Ta'zīr (discretionary punishment, such as imprisonment). So, if he poisoned him and the victim was unaware and died, there is no Qisas nor Diyah, but rather imprisonment and Ta'zīr. If he forced him to drink the poison, then Diyah is due from the 'Aqilah (male agnates). However, if he presented it to him in his drink, and he drank it of his own volition and died, there is no Diyah, but rather Ta'zīr and seeking Allah's forgiveness, because the presentation was deceptive.