Refactor the potential fun flip in HMC

[junpenglao]

Internal clean up: refactor the use age of potential function and the conversion of logdensity function to potential function in the library.

Fixes #284

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[codecov]

Codecov Report

Merging #463 (2d09392) into main (27d981e) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #463      +/-   ##
==========================================
- Coverage   99.25%   99.16%   -0.09%     
==========================================
  Files          47       48       +1     
  Lines        1872     1923      +51     
==========================================
+ Hits         1858     1907      +49     
- Misses         14       16       +2     

Impacted Files	Coverage Δ
blackjax/smc/base.py	100.00% <ø> (ø)
blackjax/adaptation/meads.py	100.00% <100.00%> (ø)
blackjax/kernels.py	99.20% <100.00%> (-0.38%)	⬇️
blackjax/mcmc/elliptical_slice.py	95.00% <100.00%> (ø)
blackjax/mcmc/ghmc.py	100.00% <100.00%> (ø)
blackjax/mcmc/hmc.py	100.00% <100.00%> (ø)
blackjax/mcmc/integrators.py	100.00% <100.00%> (ø)
blackjax/mcmc/nuts.py	100.00% <100.00%> (ø)
blackjax/mcmc/periodic_orbital.py	100.00% <100.00%> (ø)
blackjax/mcmc/proposal.py	100.00% <100.00%> (ø)
... and 5 more

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