Suggest removing the dependency requirement ggplot2 (≥ 4.0.0)

[mhyx1122]

Body:

Hi, thank you for your great work on this package.

I would like to make a suggestion regarding the current dependency requirement:

ggplot2 (≥ 4.0.0)

The ggplot2 v4.0.0 update is still not stable, and many widely used R packages that rely on ggplot2 (v3.x) have not been updated to support the new version. Because of this, forcing a requirement of ggplot2 ≥ 4.0.0 creates a long dependency chain that makes many other packages fail to load.

In my case, I spent more than three hours tracing through multiple layers of dependencies before finally identifying this version constraint as the root cause. I believe many other users may encounter similar difficulties.

For these reasons, I strongly suggest removing the strict version requirement, or at least lowering it back to a ggplot2 3.x-compatible version, unless the package has explicit features that truly require ggplot2 v4.

Maintaining compatibility with ggplot2 3.x is still important at the moment, because the ecosystem has not yet fully transitioned to ggplot2 4.x.

Thank you for considering this suggestion!

[mhyx1122]

I traced through the dependency chain and eventually found that the issue originates from ggtree, which requires ggplot2 > 4.0