Handling multiple directions at runtime

[sriharikrishna]

Here, we do the following:

1. We remove the use of nbdirsmax in the Tapenade generated code.
2. The tests are modified to not use nbdirsmax`.
3. The tests loop over different input sizes, the per-input-size logic is outlined for better code structure.
4. The following cases to do with solvers are removed because differentiating through them is the wrong approach: strsm, dtrsm, ctrsm, ztrsm, strsv, dtrsv, ctrsv, ztrsv.
5. A new file explaining the tolerances used in added.
6. The build systems (Makefiles and meson are updated)