Numpy 2 compat: replace uses of NPY_MAXARGS with a compile time constant

[neutrinoceros]

Fix #133
This is simple but fragile (it will break at runtime if numpy ever increases NPY_MAXARGS beyond the current value).
I'll open an alternative PR with a more complex and robust patch.

[neutrinoceros]

Actually my alternative patch using malloc/free, is broken.

This part works fine

diff --git a/erfa/ufunc.c.templ b/erfa/ufunc.c.templ
index a904622..85b2f9a 100644
--- a/erfa/ufunc.c.templ
+++ b/erfa/ufunc.c.templ
@@ -572,7 +572,6 @@ static int ErfaUFuncTypeResolver(PyUFuncObject *ufunc,
 {
     int *types;
     PyArray_Descr **dtypes;
-    int types_array[NPY_MAXARGS];
 
     if (ufunc->userloops) {
         Py_ssize_t unused_pos = 0;
@@ -599,10 +598,12 @@ static int ErfaUFuncTypeResolver(PyUFuncObject *ufunc,
             goto fail;
         }
         /* Copy the types into an int array for matching */
+        int* types_array = malloc(NPY_MAXARGS*sizeof(int));
         for (j = 0; j < ufunc->nargs; ++j) {
             types_array[j] = ufunc->types[j];
         }
         types = types_array;
+        free(types_array);
         dtypes = NULL;
     }

But this doesn't

diff --git a/erfa/ufunc.c.templ b/erfa/ufunc.c.templ
index 1bdbd17..6ef2128 100644
--- a/erfa/ufunc.c.templ
+++ b/erfa/ufunc.c.templ
@@ -753,7 +753,8 @@ PyMODINIT_FUNC PyInit_ufunc(void)
     PyArray_Descr *dt_ymdf = NULL, *dt_hmsf = NULL, *dt_dmsf = NULL;
     PyArray_Descr *dt_sign = NULL, *dt_type = NULL;
     PyArray_Descr *dt_eraASTROM = NULL, *dt_eraLDBODY = NULL;
-    PyArray_Descr *dtypes[NPY_MAXARGS];
+    PyArray_Descr *dtypes = malloc(NPY_MAXARGS*sizeof(PyArray_Descr));
     /* ufuncs and their definitions */
     int status;
     PyUFuncObject *ufunc;
@@ -940,6 +941,7 @@ PyMODINIT_FUNC PyInit_ufunc(void)
     status = PyUFunc_RegisterLoopForDescr(
         ufunc, {{ func.user_dtype }},
         ufunc_loop_{{ func.pyname }}, dtypes, NULL);
+    free(dtypes);
     if(status != 0){
         Py_DECREF(ufunc);
         goto fail;

(compilation fails with error C2440: '=': cannot convert from 'PyArray_Descr *' to 'PyArray_Descr')
I'll admit I'm a bit out of my depth here, and generally uncomfortable with using malloc/free to patch anything, so I'm going to open the present patch for review and let reviewers decide if a more future-proofed solution is actually needed.

[neutrinoceros]

Also: failures are thematically related in the sense that something appears to be broken in devdeps testing, but I don't think they're caused by my patch, are they ?

[mhvk]

Hmm, the maximum number of arguments the function can get is going to be a number that depends on the erfa routines, not on numpy, so we could just determine the maximum nin+nout for any erfa function, or play it safe and just replace NPY_MAX_ARGS with 32, since that obviously was large enough.

[neutrinoceros]

Oh I didn't dig enough to realise that the need didn't actually depend on numpy. I think hard-coding 32 here is sufficient. Let me push the simplest of patches !

[mhvk]

@neutrinoceros - I think part of the problem is an incorrect numpy version constraint. I just merged #122, which gets rid of that. Can you rebase to see if that resolves the errors here?