Make sync_timestamps more performant

[k1o0]

The following lines cause memory to increase and performance to decrease as the fixed offset between timestamps increases.

ibl-neuropixel/src/ibldsp/utils.py

Lines 37 to 41 in 2af823b

	tmin = np.min([np.min(tsa), np.min(tsb)])
	tmax = np.max([np.max(tsa), np.max(tsb)])
	# brute force correlation to get an estimate of the delta_t between series
	x = np.zeros(int(np.ceil(tmax - tmin) / tbin))
	y = np.zeros_like(x)

This could be resolved by first subtracting the offset between the first timestamp of both arrays, then adding it back as a constant in the interpolation function