Consider deprecating dependency on `tree`

[eb8680]

We use the handy tree utility library in a number of places throughout the codebase. Unfortunately, tree is fundamentally incompatible with support for Terms that have semantic types that are subtypes of tree.Structure (i.e. Mapping or Sequence or nested versions thereof), as it cannot identify these as non-traversable.

We should be able to replace it by adding extra patterns for defterm and defdata and making evaluate and apply use them more aggressively (see #272).

Tasks:

• Remove use of tree in ops Remove dependency of ops on dm-tree  #323
• Remove use of tree in handlers.torch
• Remove use of tree in handlers.jax and handlers.numpyro