Fix the spacing parameter processing for many modules

[seisman]

Description of proposed changes

Similar to #1804, many modules have the -I option, whose alias spacing should support passing a list like spacing=(1.0, 0.5).

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 wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• 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

[weiji14]

Also for grdproject where spacing is aliased for D, so use D="sequence" instead.

pygmt/pygmt/src/grdproject.py

Lines 21 to 34 in 5734902

	D="spacing",
	E="dpi",
	F="scaling",
	G="outgrid",
	J="projection",
	I="inverse",
	M="unit",
	R="region",
	V="verbose",
	n="interpolation",
	r="registration",
	)
	@kwargs_to_strings(C="sequence", R="sequence")
	def grdproject(grid, **kwargs):