Root finding

[danielward27]

Tidies up root finding.

We now use composition with NumericalInverse to provide a root finding method for a bijection e.g. without an analytical inverse.

This is a breaking change, specifically:

• Users explicitly calling the root finding algorithms will have to change to the new module name and functions
  (flowjax.bisection_search -> flowjax.root_finding). See the updated function names and documentation in the module.
• Users searching through the attributes of block_neural_autoregressive_flows may face a breaking change, due to the additional "layer" of composition, from NumericalInverse (another .bijection will need to be added to get to extract the BlockAutoregressiveNetwork).
• Users directly calling inverse methods on BlockAutoregressiveNetwork will now get an error, suggesting to provide an inverse method with NumericalInverse. Note, a method is provided within block_neural_autoregressive_flow.