Add new herring data object: total biomass

[grinnellm]

Will require a new script to wrangle model output from the new assessment model (SISCAH) for the PRD and SoG stocks (HG, CC, and WCVI are still in the old iSCAM format). Next year all the stocks will be in this new SISCAH format.

[andrew-edwards]

Andy doing the 2024 model output now (as need WCVI for hake assessment), but not pushing new variables (automatically called herring_spawning_biomass_2024 etc.) to GitHub as no time right now to update documentation.

Will then just unstage the changes to the herring_spawning_biomass data objects so they don't get pushed. For hake assessment , referring this time to the _2024 object. So undo that, in ecosystem-summary-hake.R.

I will then build them again when time, and by then we may as well just use the new 2025 outputs that Matt was mentioning above.

[andrew-edwards]

And Matt wanted to add total biomass also; so update the scripts and documentation as necessary.

[grinnellm]

I have code to extract age-1 and age-2 recruits from the new SISCAH model output. Same for spawning biomass, but not total biomass yet. The default is to get 5, 50, and 95% CIs as well as MPDs for each variable by year. The quantiles are calculated each time I extract the model output so it would be easy to get, say, 2.5, 50, and 97.5% CIs instead.