🗺 Add `tectonic` support

[markusritschel]

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This PR includes Tectonic as a LaTeX build engine instead of latexmk. However, I let latexmk in the code as a fallback option. The warning in packages/myst-cli/src/build/pdf/create.ts is extended with an availability check for tectonic.

See also the discussion here.

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[markusritschel]

Just added a paragraph for the documentation.

[markusritschel]

Hi @fwkoch, Tectonic should take care of it automatically. It usually figures out by itself how often it needs to run the build process. (One of its conveniences 😉).

[rowanc1]

Update: I have taken a first look at this locally and am working through some of the error states and logging, which need to change a bit if tectonic does not succeed. I will continue to chip away at this during the week.