[FR] Auto-load/unload models to save memory when unused

[NightMachinery]

Is your feature request related to a problem? Please describe.
In a shared machine, or even a personal one, it's better to automatically free up the memory used when the model is not in use.

Describe the solution you'd like
Some idle_before_unload=600 parameter that unloads the model after that many seconds of being idle. The model should be reloaded automatically whenever it is used again.

Additional context

• [Question] How would you unload a model after it has been loaded? #302