Figure: Refactor how plotting methods are attached to the Figure class

[seisman]

Motivation

In PR #3849, we're seeing many static type check errors (https://github.com/GenericMappingTools/pygmt/actions/runs/25118862756/job/73613589767?pr=3849), mainly because in pygmtlogo, we're trying to re-import the Figure class, which causes some circular imports.

Codex recommends a different way to attach the plotting wrappers to the Figure class, which can solve the static type error found in PR #3849. Changes in this PR are made by Codex.

Summary

This PR refactors how plotting methods are attached to pygmt.Figure and clarifies the role of pygmt.src.

Why

Previously, Figure methods were attached through a class-scoped from pygmt.src import (...) block in pygmt/figure.py. That worked at runtime, but it had a few drawbacks:

• It depended on package-level re-exports from pygmt/src/__init__.py just to populate Figure.
• Static analysis could misinterpret some imported names as modules instead of callables. (see the mypy errors in found https://github.com/GenericMappingTools/pygmt/actions/runs/25118862756/job/73613589767?pr=3849)
• The class-scoped import block was harder to read and maintain than explicit assignments.
• It blurred two separate concepts:
  • standalone functions that are part of the functional API
  • plotting functions that are intended to be used as methods of Figure

What changed

pygmt/figure.py

• Import each plotting callable directly from its concrete pygmt.src.* module.
• Attach these callables explicitly on the Figure class body, e.g. plot = _plot.
• Add a short comment above the attachment block to clarify the pattern.

pygmt/src/__init__.py

• Keep only standalone functions that are intended to be called directly.
• Stop re-exporting Figure-bound plotting methods from pygmt.src.
• Add a short comment explaining the distinction between standalone functions and Figure methods.

Why this is better

This makes the API structure clearer:

• pygmt.src becomes a cleaner namespace for standalone operations.
• Figure is the clear home for plotting methods.

It also improves maintainability:

• Each attached Figure method points to one explicit source module.
• The attachment logic is easier to scan and modify.
• Figure no longer depends on package-level re-export behavior for method attachment.
• The structure is friendlier to static analysis and code review.

Behavioral intent

This is intended as an internal API-structure cleanup, not a plotting behavior change. The plotting implementations themselves are unchanged; only the way they are attached/exported has been reorganized.

[seisman]

This PR is backward-compatible, but it's a big low-level refactor. Ping @GenericMappingTools/pygmt-maintainers for reviews.

Edit: Previously, it was possible to do from pygmt.src import plot, but it makes no sense to call plot as as standalone function. After this PR, from pygmt.src import plot no longer works.

[seisman]

This PR also renames the text_ method to text in commit d74da28. The name text_ was initially introduced to suppress a warning mentioned in #808 (comment).