Create a high level method for moving an entire wells completions from one date to another

Create a method from the Wells object that moves an entire set of completions for a particular date to a user specified date. This call would update the file_content_as_list for the relevant File. It would also update the dates for those specific completions.

Example call

```python
model.wells.shift_well(well_name: str, current_date: str, new_date: str) -> None:
```

Example test data for NexusWells:
From:
file_content = '''Time 01/01/2020
WELLSPEC well1
IW JW L RADW
1 2 3 5.5
1 2 4 5.5
WELLSPEC well3
IW JW L KH RADW PPERF SKIN RADB WI
137 479 3 NA 0.35400 0.5 0.00000 NA NA
137 479 4 NA 0.35400 0.5 0.00000 NA NA
137 479 5 NA 0.35400 1 0.00000 NA NA
'''

A call of model.wells.shift_well(well_name='well3', current_date='01/01/2020', new_date='01/01/2024)

Would result in:
expected_result = '''Time 01/01/2020
WELLSPEC well1
IW JW L RADW
1 2 3 5.5
1 2 4 5.5
Time 01/01/2024
WELLSPEC well3
IW JW L KH RADW PPERF SKIN RADB WI
137 479 3 NA 0.35400 0.5 0.00000 NA NA
137 479 4 NA 0.35400 0.5 0.00000 NA NA
137 479 5 NA 0.35400 1 0.00000 NA NA'''

Start at the Wells object and the relevant File's file_content_as_list; trace how dated completions are represented and updated. Use the supplied NexusWells example to verify that only well3's completions move from 01/01/2020 to 01/01/2024 and that the unchanged content remains in place.

Written by the indexing model from the issue text.