* add dependency aware cache that removed a cached node as soon as all of its decendents have executed. This allows users with lower RAM to run workflows they would otherwise not be able to run. The downside is that every workflow will fully run each time even if no nodes have changed.
* remove test code
* tidy code
* Reapply "Add union link connection type support (#5806)" (#5889)
This reverts commit bf9a90a145.
* Fix union type breaks existing type workarounds
* Add non-string test
* Add tests for hacks and non-string types
* Support python versions lower than 3.11
Currently, if a graph partially fails validation (i.e. some outputs are
valid while others have links from missing nodes), the execution loop
could get an exception resulting in server lockup.
This isn't actually possible to reproduce via the default UI, but is a
potential issue for people using the API to construct invalid graphs.
