Move to our Spack package fork.

[jhale]

This moves to our own Spack package repo which is a fork of the builtin repo.

In the near future, we should probably implement our own package repo as an overlay to the builtin repo. This would allow us to roll out, and test, Spack releases of FEniCS before merging them onto the builtin repo. Additionally, we would not need to manually bump our own builtin repo branch.

During this process, I discovered that +hypre for PETSc is causing PETSc to concretise to an old version. Inspecting the package.py, it is not clear why this happens. For now, ^petsc~hypre is set.

[jhale]

PETSc is failing to build due to an old version of Hypre (which is in the cache). However, the Spack package file for PETSc precludes this. Unclear.

[jhale]

Wildly different pressure norm for the monolithic direct solve.

----------------------------- Captured stdout call -----------------------------
(A) Norm of velocity coefficient vector (high-level nested, iterative): 17.47837016420078
(A) Norm of pressure coefficient vector (high-level nested, iterative): 311.4425379648746
(A) Norm of velocity coefficient vector (low-level nested, iterative): 17.47837016420078
(A) Norm of pressure coefficient vector (low-level nested, iterative): 311.4425379648746
(B) Norm of velocity coefficient vector (blocked, iterative): 17.478370164287277
(B) Norm of pressure coefficient vector (blocked, iterative): 311.44253796470696
(C) Norm of velocity coefficient vector (blocked, direct): 17.478367449917705
(C) Norm of pressure coefficient vector (blocked, direct): 311.44253044039357
(D) Norm of velocity coefficient vector (monolithic, direct): 17.468884396369752
(D) Norm of pressure coefficient vector (monolithic, direct): 1193.2978766802526
----------------------------- Captured stderr call -----------------------------
Traceback (most recent call last):
  File "/__w/dolfinx/dolfinx/dolfinx-src/python/demo/demo_stokes.py", line 672, in <module>
    np.testing.assert_allclose(norm_u_4, norm_u_0, rtol=1e-4)
  File "/opt/view/lib/python3.12/site-packages/numpy/testing/_private/utils.py", line 1715, in assert_allclose
    assert_array_compare(compare, actual, desired, err_msg=str(err_msg),
  File "/opt/view/lib/python3.12/site-packages/numpy/testing/_private/utils.py", line 921, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Not equal to tolerance rtol=0.0001, atol=0

Mismatched elements: 1 / 1 (100%)
Max absolute difference among violations: 0.00948577
Max relative difference among violations: 0.00054271
 ACTUAL: array(17.468884)
 DESIRED: array(17.47837)

[jhale]

hdf5+hl fix pushed upstream spack/spack-packages#2402

[jhale]

Above issue fixed - note that SuperLU is probably unsuitable for a problem with a nullspace.