refactor(generator/rust): factor out some common execute code

[codyoss]

Had to create a NoBody type to pass along to satisfy generics. This type is not exported.

Fixes: #139

[codyoss]

@coryan The spell check is a false positive. Not sure how to get around that...

There is a .typos.toml file you can add directives to:

https://github.com/crate-ci/typos/blob/master/README.md#false-positives

https://github.com/crate-ci/typos/blob/master/docs/reference.md

[coryan]

This worked for me:

[type.mustache]
extend-glob = ["*.mustache"]

[type.mustache.extend-words]
ser = "ser"