Implement symbolic minimize and root Ops (#1182)

* Implement `optimize.minimize`

* Add more tests

* Code cleanup

* Add RootOp, fix gradient tests (they are failing)

* Correct gradients for `minimize`

* Mypy

* remove debug flag

* minimize works

* Implement minimize_scalar

* Use LRU cache wrapper for hessian option

* Remove useless Blockwise

* Feedback

* use truncated_graph_inputs and refactor

* Implement Root Op

* Factor out shared functions

* Implement `root_scalar`

* mypy 😍

* Add specialized `build_fn` to each Op to handle scipy quirks

* Changes to support float32 inputs

* Check inputs to RootOp

* More mypy

* Fix bug when minimize gets scalar input

Author: jessegrabowski