Update the `Met2dDataFile` class hierarchy to use `unique_ptr` to improve memory management

[JohnHalleyGotway]

Describe the Task

SonarQube flags many instances of the MET C++ code managing its own memory through calls to new and delete. The std::unique_ptr() silences these warnings and helps to prevent memory leaks.

While the VarInfo class hierarchy was recently updated to make use of unique_ptr, recommend making similar changes to the Met2dDataFile class hierarchy.

Time Estimate

1 day

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