Mismatch computation should not use values from raw times with smryh

[berland]

In this part of the code:

fmu-ensemble/src/fmu/ensemble/observations.py

Line 280 in 5269d5e

# Will use raw times when available.

the smryh calculation will use all timesteps available in the raw UNSMRY files, which will give unpredictable weighting. It also removes the possibility of controlling the points in time used if the user has done load_smry(time_index='last') prior to mismatch calculation.

credit: rnyb

[berland]

The time_index must be specified by the user in the smryh case, either in the observation dictionary alongside key and histvec, or/and in the mismatch() function call.

When issue #51 is solved, load_smry() and then virtualization of the ensemble will be a workaround.