Add all datafile functions (+needed dependent functions)

[madebr]

This improved datafile allows us to write back brender data structures to disk.
This also includes reading/writing text representations of the brender structures.
I added a substantial amount of tests for this.

This pr adds the following:

• adds fixed functions/macros in fixed.c/fixed.h. This allows to hide the many conversion factors to convert fixed to float numbers.
• implement all scratch functions since datafile uses these
• my math pr Implement all brender matrix functions #66 did not actually build the tests, so fix this
• BrFilePrintf was missing + BrVSprintfN wasn't returning anything
• Add the ability to the test suite to create temporary files since datafile needs to be able to write to disk.
  These files are created in a process dependent folder (it includes the process id).
  On Linux, this creates e.g. the /tmp/dethrace_test_5408/ folder.

Output of github actions: https://github.com/madebr/dethrace/actions/runs/1731316005