Support magic TeX comments

[koppor]

TeXStudio suports [magic comments]:

% !TeX program = lualatex
% !BIB program = biber

When these magic comments are present, lualatex and biber are used as compilers.

In case ltx2any would recognize these, it could be used "seamlessly" as LaTeX build tool without any additional configuration ("knobless use").

[reitzig]

biber should be chose automagically. 🤔 If not (do you have an MWE?) Biber.do? needs an update. Happy to accept a PR in that case!

Selecting the appropriate TeX program (which I call "engine" here 🫣) from the file sounds reasonable to me; if we can avoid having to specify a CLI flag, I'm all for it! Happy to accept a PR!