Add tests for `scipy.sparse.csgraph` and `scipy.sparse.linalg`

[mtsokol]

Hi @hameerabbasi,

Here's a PR that contains:

• Moved test_unary[sign((x_i is -0 or x_i == +0)) -> 0] to skips as this test is now flaky (it correctly failed in the PR but I see in the main branch it succeeded causing XPASS, so I guess --derandomize didn't get rid of all randomness)
• test_scipy_sparse_csgraph_dispatch with scipy.sparse.csgraph tests
• commented out a few linalg tests that require https://github.com/scipy/scipy/pull/20759 (and a new scipy release)
• test_scikit_learn_dispatch, skipped for now as it requires https://github.com/scikit-learn/scikit-learn/pull/29031

[github-actions[bot]]

Test Results

5 991 tests  +68   5 932 :white_check_mark: +40   9m 32s :stopwatch: -11s     1 suites ± 0      59 :zzz: +28      1 files   ± 0       0 :x: ± 0 

Results for commit 1839415d. ± Comparison against base commit 554cc7bc.

This pull request removes 8 and adds 76 tests. Note that renamed tests count towards both.

``` sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Finch-coo-C] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Finch-coo-F] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Finch-csc-F] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Finch-csr-C] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Numba-coo-C] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Numba-coo-F] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Numba-csc-F] sparse.tests.test_backends ‑ test_scipy_sparse_dispatch[BackendType.Numba-csr-C] ``` ``` sparse.tests.test_backends ‑ test_scikit_learn_dispatch[BackendType.Finch-csc_matrix-csc-F] sparse.tests.test_backends ‑ test_scikit_learn_dispatch[BackendType.Numba-csc_matrix-csc-F] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Finch-coo_matrix-coo-F] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Finch-csc_matrix-csc-F] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Finch-csr_matrix-csr-C] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Numba-coo_matrix-coo-F] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Numba-csc_matrix-csc-F] sparse.tests.test_backends ‑ test_scipy_breadth_first_tree[BackendType.Numba-csr_matrix-csr-C] sparse.tests.test_backends ‑ test_scipy_connected_components[BackendType.Finch-coo_matrix-coo-F] sparse.tests.test_backends ‑ test_scipy_connected_components[BackendType.Finch-csc_matrix-csc-F] … ```

This pull request skips 3 and un-skips 1 tests.

``` sparse.numba_backend.tests.test_compressed ‑ test_reductions_float16[f4-None-sum-kwargs0] sparse.numba_backend.tests.test_compressed ‑ test_reductions_float16[f8-None-sum-kwargs0] sparse.numba_backend.tests.test_coo ‑ test_reductions_float16[f4-None-sum-kwargs0] ``` ``` sparse.numba_backend.tests.test_coo ‑ test_reductions_float16[i4-axis4-mean-kwargs1] ```

:recycle: This comment has been updated with latest results.

[hameerabbasi]

Thanks for working on this @mtsokol!