Show test execution times in pytest

[seisman]

Description of proposed changes

Show the slowest tests with executation times > 0.2 s (the default is 0.005 s).

Reference: https://docs.pytest.org/en/stable/usage.html#profiling-test-execution-duration

Addresses #584

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[seisman]

Now we know the slowest tests:

============================== slowest durations ===============================
4.48s call     tests/test_coast.py::test_coast_aliases[png]
3.38s call     tests/test_grdview.py::test_grdview_with_perspective_and_zaxis_frame[png]
2.45s call     gridops.py::pygmt.gridops.grdfilter
2.19s call     tests/test_coast.py::test_coast_world_mercator
2.06s call     tests/test_figure.py::test_shift_origin
1.91s call     src/inset.py::pygmt.src.inset.inset
1.74s call     tests/test_coast.py::test_coast_dcw_state[png]
1.69s call     tests/test_inset.py::test_inset_aliases[png]
1.60s call     tests/test_logo.py::test_logo_on_a_map[png]
1.59s call     tests/test_plot.py::test_plot_from_file
1.57s call     tests/test_coast.py::test_coast_dcw_continent[png]
1.45s call     tests/test_coast.py::test_coast_dcw_list[png]
1.44s call     tests/test_coast.py::test_coast_dcw_multiple[png]
1.44s call     tests/test_grdcontour.py::test_grdcontour_labels[png]
1.42s call     tests/test_plot3d.py::test_plot3d_from_file[png]
1.42s call     tests/test_grdimage.py::test_grdimage_shading_xarray[True-png]
1.41s call     tests/test_grdimage.py::test_grdimage_shading_xarray[+a30+nt0.8-png]
1.35s call     tests/test_coast.py::test_coast_dcw_single[png]
1.35s call     tests/test_coast.py::test_coast_iceland[png]
1.32s call     tests/test_config.py::test_config
1.16s call     tests/test_basemap.py::test_basemap_winkel_tripel
1.14s call     tests/test_coast.py::test_coast
1.13s call     tests/test_colorbar.py::test_colorbar_shading_string[png]
1.12s call     tests/test_colorbar.py::test_colorbar_shading_float[png]
1.10s call     tests/test_colorbar.py::test_colorbar_shading_list[png]

[weiji14]

Nice! Surprising how so many of the fig.coast tests are slow. This will definitely help with #584 down the track.