GridPlan order issue

[fdrgsp]

from #149

Small problem I see is for this sequence:

>>> seq = MDASequence(axis_order="gtc",time_plan={"interval": 1, "loops": 2},channels=[{"config": "DAPI", "exposure": 1}],grid_plan={"rows": 2, "columns": 2})
>>> for event in seq:
...    print(event)
...
index=mappingproxy({'t': 0, 'g': 0, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=0.0 x_pos=-0.5 y_pos=0.5
index=mappingproxy({'t': 1, 'g': 0, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=1.0 x_pos=-0.5 y_pos=0.5
index=mappingproxy({'t': 0, 'g': 1, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=0.0 x_pos=0.5 y_pos=0.5
index=mappingproxy({'t': 1, 'g': 1, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=1.0 x_pos=0.5 y_pos=0.5
index=mappingproxy({'t': 0, 'g': 2, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=0.0 x_pos=0.5 y_pos=-0.5
index=mappingproxy({'t': 1, 'g': 2, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=1.0 x_pos=0.5 y_pos=-0.5
index=mappingproxy({'t': 0, 'g': 3, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=0.0 x_pos=-0.5 y_pos=-0.5
index=mappingproxy({'t': 1, 'g': 3, 'c': 0}) channel=Channel(config='DAPI') exposure=1.0 min_start_time=1.0 x_pos=-0.5 y_pos=-0.5

Might no be a very typical setup with axis order "gtc, but note how the min_start_time resets for every g index. This leads to the first time series at position 0 respecting the interval, while all later positions are acquired at max speed.