Refactor TEX and SVG temporary files to use stdin

[a1-su]

Proposed Changes

This PR refactors the returnPDF, exportTimetablePDFResponse, and graphImageResponse to use stdin instead of the temporary, intermediate .tex and .svg files it was using previously. Instead of creating the temporary files, the tex and svg contents are directly being piped into the pdflatex and magick processes.

Note that while returnPDF in Controllers/Timetable.hs now entirely uses stdin instead of tex temporary files, createImageFile in Export/ImageConversion.hs still uses temporary svg files and the new withImageFile function handles piping the svg contents instead, because the temporary svg is still required for renderTableHelper in Export/TimetableImageCreator.hs.

Type of Change

(Write an X or a brief description next to the type or types that best describe your changes.)

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)	X
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)

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Questions and Comments

(Include any questions or comments you have regarding your changes.)

• There are some odd remnants of the old code that I can change depending on what is seen fit. Notably, in Export/PdfGenerator.hs, the createPDF function used two-space tabs instead of four, and has the "Waiting for a process..." and "Process Complete" logs which I can remove should it be unneeded.

[coveralls]

Pull Request Test Coverage Report for Build bfc72401-527a-4903-9f9c-00af9c843ae6

Details

• 0 of 11 (0.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 56.478%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/Controllers/Graph.hs	0	4	0.0%
app/Export/ImageConversion.hs	0	7	0.0%

Totals
Change from base Build ac1c0723-45d7-45be-8bea-efc2c6525e84:	-0.05%
Covered Lines:	2280
Relevant Lines:	3960

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💛 - Coveralls

[david-yz-liu]

Nice work @a1-su, I just left a few comments. Modifying the indentation of createPDF is okay here, as you modifying the overall function content quite a bit.

[david-yz-liu]

Yes I think you can delete these logging calls (throughout)

[david-yz-liu]

Now that this function is not writing to a file, I think we should be able to make it pure ([String] -> Text)