pygmt.dataset.load_*: Add type hints for the 'region' parameter

[seisman]

Description of proposed changes

In the previous version, region can be either a list or a string, but a string like region="0/10/0/20" is not Pythonic and a tuple like region=(0, 10, 0, 20) is also accepted.

This PR adds type hints to the region parameter of load_* functions. The region parameter must be a Sequence type (list, tuple, or array). A string type is still supported but no longer documented/recommended.

Preview: https://pygmt-dev--3272.org.readthedocs.build/en/3272/api/generated/pygmt.datasets.load_earth_age.html#pygmt.datasets.load_earth_age

[seisman]

Will apply the same changes to other load_* functions if @GenericMappingTools/pygmt-maintainers agree with the changes.

Edit: Applied to all load_functions in 4ddf1f9

[seisman]

This line can be removed because region is passed to _load_remote_dataset and in that function region can be a sequence.

[yvonnefroehlich]

Passing a list or a tuple is definitely more Pythonic.
But I am wondering how we want to handle arguments containing ISO codes and arguments extending a region via appending +r, e.g., lon_min/lon_ma/lat_min/lat_max+rincrement or ISO_code+rincrement. Here, we still need a string input.

[seisman]

But I am wondering how we want to handle arguments containing ISO codes and arguments extending a region via appending +r, e.g., lon_min/lon_ma/lat_min/lat_max+rincrement or ISO_code+rincrement. Here, we still need a string input.

That's a good point.

lon_min/lon_ma/lat_min/lat_max+rincrement

I don't think GMT's -R option has such syntax (see https://docs.generic-mapping-tools.org/dev/gmt.html#r-full). -Rxlleft/ylleft/xuright/yuright+r is close to this one, but it's mainly for specifying a region for oblique projections. So, I guess the syntax doesn't make sense here.

ISO_code+rincrement

This one should be supported currently. We probably should implement the ideas in #2646 and then people should use the proposed to dcw module to get the region before passing to the region parameter.

Anyway, I'll add the string type back. Added back in 9c2ac53.

[yvonnefroehlich]

lon_min/lon_ma/lat_min/lat_max+rincrement

I don't think GMT's -R option has such syntax (see https://docs.generic-mapping-tools.org/dev/gmt.html#r-full). -Rxlleft/ylleft/xuright/yuright+r is close to this one, but it's mainly for specifying a region for oblique projections. So, I guess the syntax doesn't make sense here.

You are totally right; such a syntax is not available, and your guess is what I was actually thinking about. I must have gotten confused during writing - I apologize for the confusion!