Pretty much had the same issue and wanted to just keep my firepit lit.
But since I´m currently getting into VS modding, I made a very basic mod that enables just that.
I changed aged firewood to a slow burning fuel thats too low heat do cook anything, and added some crafting recipes.
For compatibility i didn´t want to change the name of aged firewood, but i might look into making a texture and create a "treated firewood" later on instead
https://mods.vintagestory.at/slowfuel
PS: In general, as long as the firepit is empty, fuel lasts 2.5x as long.