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]

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 ⚠️
internal/services/store/store.go	65.88%	20 Missing and 9 partials ⚠️
cmd/internal/exec.go	25.00%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@            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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