fix: javadoc for the isthmus library

[mbwhite]

No description provided.

[benbellick]

I think this change is broadly good, but I worry about such a large diff in one small PR. I am not remotely familiar with the calcite stuff, so I wouldn't be able to judge the accuracy of these comments.

But I wonder if it would be easier to get this one in if it was broken up over multiple PRs, perhaps talking a file or two at a time. What do you think about that?

[mbwhite]

I think this change is broadly good, but I worry about such a large diff in one small PR. I am not remotely familiar with the calcite stuff, so I wouldn't be able to judge the accuracy of these comments.

But I wonder if it would be easier to get this one in if it was broken up over multiple PRs, perhaps talking a file or two at a time. What do you think about that?

Sadly I've not been able to pay much attention to this PR in the last couple of months due to other priorities - but yes I had this exact conversation with @nielspardon; the next PR with JavaDoc will just have 1 class :-)

[mbwhite]

Creating a subset of PRs each with a few files... (to make review easier - I'm not trying to make my PR stats look better :-))

#754
#755
#756
#758
#759
#760
#761
#762
#763
#764
#765
#766