ninja-0001: depfile_parser.cc std::find over ins_/outs_ vectors is O(N) per
token → O(N²) total parse; fix adds unordered_set ins_seen_/outs_seen_ members
to DepfileParser for O(1) duplicate detection (490x at N=1000).
ninja-0002: graph.cc std::find_if over edge->outputs_ called for each depfile
output token is O(M×N); fix builds unordered_set from edge outputs once before
the loop for O(M+N) total (125x at M=N=500).
