add helper function for converting existing functions to tasks

[satra]

right now we have decorators in pydra.mark, which are useful when defining a pydra task directly.

but we can also use them in this form to decorate any arbitrary library function:

pydra_task = task(annotate(...)(function))()

it would be nice to have a simple helper that looked like:

taskify(function, annotation=None) which would internally do the decoration.

this serves the same function as the decorators and can use the decorators internally, but is easier to read and create.

[satra]

it should be possible through inspection to annotate both inputs and outputs of a function automatically.

pydra_task = taskify(python_function) should do a reasonable thing out of the box, even for outputs (using internal variable names in a return statement). this obviously won't provide any validation or conversion or additional metadata support without extended function annotation, but would allow people to immediately insert pydra caching and split combine into existing scripts, even without using workflows.

[tclose]

this is possible in new syntax