Add getters for Laplacian flags

[ZedThree]

These methods allow us to make the {global, inner_boundary, outer_boundary}_flags members private in Laplacian. This combo silences a whole bunch of clang-tidy warnings, mostly around implicit comparison between int and bool. One extra change was to stop passing the flags into tridagMatrix -- this was a bit redundant as it's a private method on Laplacian anyway, so we were passing members to a method.

While checking all this, I found that the LaplaceSPT dtor crashed clang-tidy, mostly likely because it was doing some pointer address fiddling. I've also fixed that, which also fixes a couple of other issues at the same time.