For Day19, if you have a slighlty weaker computer, or a fanless, I encourage you to build the binary with shards build --release --no-debug and run the binary, so that it completes quickly. Day19 Part2 doesn't finish on my Surface Pro 7 i5 with no fan.
Surface Pro 7 with i5, fanless, 8gb ram
shards build --release --no-debug
Total runtime of all 25 days: 22.76s
Total runatime without day 19: 6.94s