regression.py: Exchange checkpointing for parallelism (#15)

* regression.py: Exchange checkpointing for parallelism

Since I have the vague feeling that regression has to be rewritten in the future
anyway, all of these changes have been LLM generated.

For now, my priority is understanding whether or not the 100 Great Theorems are
broken or not.

* Use two cores for standard regression testing

* build-instructions.sh: python -> python3

Seems like Debian does not have this symlink by default.

Author: dnezam

build-instructions.sh

@@ -26,7 +26,7 @@ make
 ./cake --types < /dev/null > types.txt 2>&1
 
 # Generate candle_insulate.ml
-python ../insulate.py types.txt insulate.ml
+python3 ../insulate.py types.txt insulate.ml
 
 #  The working directory of the binary will be CANDLE_ROOT/candle/build,
 #  so it needs to change directory to CANDLE_ROOT after booting..