Fix encoders with inner multi_temporal_strategy when using LTAE

[gle-bellier]

Error:

• Some encoders (e.g. satlasnet_mi) already merge information on the temporal dimension. Then, no multi_temporal_strategy is needed; if one is included in the configs, it will be skipped.
• When using the LTAE, the decoder input channels are changed to match LTAE output channels (LTAE only works with all inputs having the same number of channels)
• The bug was that even if the LTAE was skipped, the decoder's input channels were modified, causing shape errors.

Fix: change decoder input channels if LTAE is used AND the encoder has a multi-temporal output.
(for both SegMTUPerNet and RegMTUPerNet)