The client registers Functions, but the decorator that packages one was
called `udf` and produced a `UdfDefinition`. Rename them to `function`
and `FunctionDefinition`, and say "function" instead of "UDF" in the
docstrings, error messages and docs around them.
`udf` and `UdfDefinition` stay as deprecated aliases that emit a
`DeprecationWarning`. The source packager strips either spelling of the
decorator, so `@udf` and `@function` produce the same artifact and
digest, and the wire contract is unchanged. DataFusion and Lance UDF
types, and Geneva's `@udf` in the integration docs, are unrelated and
untouched.
Wyatt Alt
b5c5ede39f