fix: prefer map[string]any everywhere where we don't actually need to use DeepCopy

[krancour]

Follow-up on #2589

The change wasn't as safe as I thought.

This is a more holistic fix that switches the output from promotion steps from a State to a regular map[string]any.

The only benefit a State has over a normal map[string]any is a few convenience methods, including DeepCopy(). We only need that at the top of the state map. i.e. There's no reason that output from individual steps can't be a normal map.

I can vouch for this fix better than I could for #2589 because when this is combined with #2590, I can now observe most of the Git-based promotion steps working together correctly from end-to-end.

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 8 lines in your changes missing coverage. Please review.

Project coverage is 51.10%. Comparing base (16e4674) to head (3b19562).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/directives/argocd_revisions.go	0.00%	3 Missing ⚠️
internal/directives/git_pr_waiter.go	25.00%	3 Missing ⚠️
internal/directives/git_pr_opener.go	75.00%	1 Missing ⚠️
internal/directives/simple_engine.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2591   +/-   ##
=======================================
  Coverage   51.10%   51.10%           
=======================================
  Files         282      282           
  Lines       20945    20945           
=======================================
  Hits        10703    10703           
  Misses       9578     9578           
  Partials      664      664           

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