incompatible with av version 14.* (variable_fps AttributeError)

[bjudkewitz]

Using av version 14.*, VideoReader init fails with

AttributeError: 'av.format.ContainerFormat' object has no attribute 'variable_fps'

Not a major problem as long as av < 14 (dependency lilsts were updated), but may have to be revisited in the future.

[bjudkewitz]

PyAV-Org/PyAV#1741

[bjudkewitz]

It seems like variable_fps support was dropped by the libav library. One solution is to drop this check and remove these two lines:

daio/src/daio/video.py

Lines 29 to 30 in ea2d8d4

	if self.container.format.variable_fps:
	warn_transcode(f'Variable frame rate video detected. Seeking will likely be unrealiable. I will warn again if I detect seek gitches')

We are separately checking for mismatches between expected and actual pts anyway, so dropping this specific check might be acceptable