Add NMFS-branded ggplot2 themes

[jonpeake]

The new ggplot2 update (https://www.tidyverse.org/blog/2025/09/ggplot2-4-0-0/) provides an overhaul to ggplot custom themes, allowing for easier incorporation of default palettes, fonts, styles, etc. It might be a good idea to incorporate some of the new features into nmfspalette. A standard NMFS ggplot theme could be a great place to start.

[jonpeake]

Related to https://github.com/nmfs-ost/nmfspalette/issues/34

[sbreitbart-NOAA]

Hi Jon- thank you for sharing these updates! I'll certainly work on updating the package to adapt to the new changes.