Renable nested title additions and amend test with frontmatter

[seam345]

The frontmatter changes broke the add_titles test

I haven't fully understood the changes you made but going purely off the test I assume you would prefer the result to be

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title: Main note
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# Main note

# Sub note

# Sub sub note

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instead of

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title: Main note
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So I have made the code changes to achieve this and updated the expected test result

Btw the input file is this

Hope I understood your goal right, I'm just currently attempting to follow in your footsteps to publish a section of my obsidian vault but trying to codify your steps with a Nix file and building a Rust packages in nix requires all tests to pass :D

[seam345]

Oh I see this is making use of the --add-titles argument, would you prefer instead of overriding the current --add-titles we could add an --add-frontmatter-titles?