POC feat(template): add Objects.{WithState,WithAgentState,WithSeedRegistryState}

[mkcp]

Description

This is a proof of concept / WIP branch to explore adding Zarf builtins to template.Objects for the new go-templating.

Related Issue

Fixes #4226
Relates to #3946

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov]

Codecov Report

❌ Patch coverage is 78.89908% with 23 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/internal/template/template.go	78.89%	16 Missing and 7 partials ⚠️

Files with missing lines	Coverage Δ
src/internal/template/template.go	79.78% <78.89%> (-1.23%)	⬇️

... and 10 files with indirect coverage changes

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