Add find_MAP with close JAX integration and fix bug with Laplace fit (#385)

* Add JAX-based `find_MAP`

* add `better_optimize` to CI envs

* Fix relative import

* Remove `find_MAP` import from module-level `__init__.py`

* Update docstring

* Allow calling `find_MAP` inside model context without model argument

* Required patched better_optimize

* in-progress refactor

* More refactor

* Generalize code to use any pytensor backend

* Reconcile the two laplace approximation functions

* Use absolute import in doctest

* Fix imports

* Fix unrelated statespace test

* - Rename argument `use_jax_gradients` -> `gradient_backend`
- Rename function `laplace` -> `sample_laplace_posterior`

* Fix typo introduced by rename refactor

* use `mode=FAST_COMPILE` to get `unobserved_value_vars` after MAP optimization

* Rename `test_jax_find_map.py` -> `test_find_map.py`

* Improve docstring for `fit_laplace`

* Update tests to match new signature

* Update docstring

Author: jessegrabowski

Diff for: conda-envs/environment-test.yml

@@ -13,3 +13,4 @@ dependencies:
   - pymc>=5.17.0  # CI was failing to resolve
   - blackjax
   - scikit-learn
+  - better_optimize>=0.0.10

Diff for: conda-envs/windows-environment-test.yml

@@ -13,3 +13,4 @@ dependencies:
   - pymc>=5.17.0  # CI was failing to resolve
   - blackjax
   - scikit-learn
+  - better_optimize>=0.0.10