Boilers should have a warm-up period

Recently in a discussion about Thermal Storages in Discord, we realized that they don't really provide much of a benefit, since you can just use coal buffers for boilers and the boilers will pretty much instantly respond to spikes in steam usage. So to make thermal storages actually quite useful, my suggestion is that boilers will have a similar warm-up period as generators have. When idle, they'll cool down and when cool they would produce Steam at either a worse ratio (more coal consumed per unit of water) or simply running a lot slower.

This would both be more realistic as well as making thermal storages useful as Steam buffers since generators now can't immediately kick in and fill up any spikes in Steam demand.