Feature request: per-call field overrides for FakeData

Feature request: per-call field overrides for FakeData: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I'm using faker to populate structs in unit tests. Most of the time the default tag-based generation is exactly what I want, but I keep running into two cases…

The task

I'm using `faker` to populate structs in unit tests. Most of the time the default tag-based generation is exactly what I want, but I keep running into two cases where I need finer control on a **per-call** basis:

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.