Feedback Energy Injection Changes

This MR includes:

• A limiter for the diffusion in ANARCHY-DU that enables feedback in EAGLE to work
• Minor fixes to some hydro test scripts that were broken that I came across
• Adds a script to the FeedbackEnergy_3D test to plot energy as a function of alpha_diff.

added 2 commits

• d03cdf4d - Tidied up the min/max in diffusion alpha setting
• e7b64142 - Formatting

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resolved all discussions

merged

mentioned in commit 57f2253e