length-only: size=1 previous=10 get(zz)=20 contains(zz)=true
remove(zz): empty=true
length-then-text: keys=[c, aa, bb] contains(zz)=false
list-sort: [c, bb, aa]; size=3
decimal: equals=false compareTo=0 hash-size=2 tree-size=1
PASS 83 checks; fixed keys, no concurrency or performance claim
