Add min_fixation_duration_threshold in interface

[kalaschnik]

This is helpful to exclude microfixations, which I-VT may classify as fixations but cannot be processed by humans:

The duration of 80-90 milliseconds is considered to be the shortest fixation that humans can control and process cognitively (Galley et al., 2015; Holmqvist & Andersson, 2017). Fixations shorter than that serve in the general perceptional process but the individual is unaware of them (Galley et al., 2015).

Furthermore, since we use intra_scope_window cut, this can also create fixations even smaller than 50... this would also catch those falsy fixations

[kalaschnik]

Literature:

• https://helda.helsinki.fi/bitstream/handle/10138/324085/haataja_eeva_dissertation_2021.pdf?sequence=1