Energy inference cleanup

[zaqqwerty]

While working on #173, there were a lot of changes that are tangential to #115 but do simplify the code. I forked these changes off into this PR.

• Separate EnergyInference into an interface class and a default methods class
• Add hook for adding code to be called at the start of every inference function (will be used to automate infer calls)
• Improve seed handling, tracing them now works (no need to re-define sample wrappers anymore)
• Explicitly create distributions instead of using a distributions layer
• Remove persistent keyword in GradientTape of expectation call for now. Did this since persistence seems to cause issues with TFQ, see https://github.com/google/qhbm-library/pull/163#issuecomment-1034053388 ; can revisit in #157
• Simplify tf.function wrapping
• Manage more test constants in setUp method