FidelityChannels

Data processing: a shared channel can only raise the fidelity

3/3 passed in 4ms

Test	What it does	Result
test_coherent_loss	Pure loss scales a coherent pair's amplitude difference by $\sqrt{T}$, so $F$ goes from $\exp (-|d{|}^2/2)$ to $\exp (-T|d{|}^2/2)$ -- an equality, not a bound.	✅ pass
test_noise_monotone	A shared thermal-loss channel never lowers $F$, over a grid of $(T,\xi )$ at both planes.	✅ pass
test_thermal_channel	Two thermal states converge as $T$ falls, both reaching the vacuum with $F\to 1$.	✅ pass