excessive memory use

[travisstaloch]

results running a little benchmark script which diffs 2 slightly different Sema.zig files:

• 100 diffs - results in the process being OOM killed.
• 20 diffs -

$ zig build test -fsummary -Dalgo=diffzimilar
run test: error: diffzimilar=6.197s diffs.len=12
Build Summary: 4/4 steps succeeded; 1/1 tests passed
test success
└─ run test 1 passed 6s MaxRSS:451M
   ├─ zig test Debug native success 1s MaxRSS:230M
   │  └─ options cached
   └─ zig test Debug native (+1 more reused dependencies)