Topic/multi pick and memoization

[charleswoerner-wayve]

Add support for new MultiPick extension command. Add support for memoization of shellCommands so that the computation can be reused (and remain stable) across multiple references within the same command evaluation scope. Internally, I refactored to extract a Resolver class within the UserCommandsController to enable command-scoped caching to avoid cache conflicts between simultaneously running async functions. Additionally, MultiPick selections are persisted across command invocations.

As implied by the documentation changes, the use case here is to support the selection of a subset of PyTest tests invoked via a runnable PyTest target under Bazel. I wanted to be able to invoke a runnable PyTest target in --collect-only mode, filter out the list of PyTest cases, present them to the user as a multi-pick selector, then take the selected items and append them to a Bazel PyTest test command to run the selected tests. Options such as --no-cov have to be able to be toggled in order to disable coverage thresholds when running just a few tests.

This addresses the feature request I created in #30

[charleswoerner-wayve]

@jabbottn Hi Josh, I worked out an implementation for a few proposed enhancements to better support some of the more complex setups we envisioned at work.

[cwoerner]

@jabbottn Thoughts about merging this multi-pick feature?