feat: add key-value store for sharing data across executables

[jahvon]

Includes the addition of a flow store subcommands that can be called within shell executables to set/get data that may be set within other executables.

Be default, the commands when called outside of an executable will store values into a "root bucket" whose values are accessible in all executables. When running serial or parallel exec, a separate temporary bucket is created for sharing data across that execution run.

This is still experimental; docs updates to come

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 58.09524% with 88 lines in your changes missing coverage. Please review.

Project coverage is 35.36%. Comparing base (fd5bbc7) to head (0ceabdc). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/internal/store.go	55.35%	40 Missing and 10 partials :warning:
internal/services/store/store.go	65.88%	20 Missing and 9 partials :warning:
cmd/internal/exec.go	25.00%	6 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #187 +/- ## ========================================== + Coverage 34.64% 35.36% +0.71% ========================================== Files 81 83 +2 Lines 6742 6956 +214 ========================================== + Hits 2336 2460 +124 - Misses 3968 4039 +71 - Partials 438 457 +19 ```

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