feature/sc 42001/add constructor

[sunayana]

This story is now complete and ready for review, it implements:

• Constructor for c++ Depression class
• Wraps constructor with libcxxwrap-julia
• Implement push_back and constructor in C++ DepressionHierarchy
• Modifies RichDEM.jl to accomodate this.
• The corresponding Julia code documenting how these methods work can be found in the usual Notion page.

[shortcut-integration]

This pull request has been linked to Shortcut Story #42001: Add constructor for Depression in richdem.

[croissant-tmp]

LGTM! Live demo showed that it worked very well!

More changes were added to this branch and it is now complete with all requirements of the story. It would be good to review it once again.

[sunayana]

The issue which we see is that the conversion from CxxDepression to julia Depression consistently fails for the member field dep_label. My guess is, this is happening because on the C++ side dep_label appears right after std::vector<uint32_t> ocean_linked. The way std::vector stores values in memory is not contiguous but what we have is just a pointer to the first element of the vector. Since we only get one pointer to CxxDepression we are possibly getting garbage value dep_label. The only way I see currently to resolve this issue is to use the C++ member methods that I have defined in jldepressions.cpp, and also a similar strategy used in libcxxwrap-julia for Foo struct here
Hence I will proceed along those lines here as well.