Better support for caching / checkpointing development workflow - umbrella issue about hamilton HOT 2 OPEN

I took one of the targets examples and transferred it one-to-one to hamilton to see how the concepts compare. Both workflows are implemented in modules and make use of helper functions from a separate module. Then both are started interactively from quarto documents and their results and graphs visualized in the rendered output of said notebooks: http://jmbuhr.de/targets-hamilton-comparison/ (source code: https://github.com/jmbuhr/targets-hamilton-comparison)

Again, this is for exploration of possibilities, not to impose paradigms on you :)

In this first pass I noticed two things I was missing in hamilton compared to targets when it comes to caching:

• changing a function that is used by a node, but is not itself a node, should also invalidated the cache of the node
• loading the cached result from any node independently of the dr.execute run as with tar_load(<name of node>) (https://docs.ropensci.org/targets/reference/tar_load.html) is super helpful for interactively picking up where you left of with a workflow and working on different parts of it.

from hamilton.

For inspiration, the developer documentation of how targets does caching might come in handy: https://books.ropensci.org/targets-design/data.html#skipping-up-to-date-targets

from hamilton.