84469 Migrate build_macos and web_test_compiler to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

84820 Audit devicelab log streaming for nullability (team, a: accessibility, cla: yes, waiting for tree to go green, a: null-safety)

84840 fix _owner nullability in routers.dart (framework, cla: yes, f: routes, will affect goldens, a: null-safety)

85242 Migrate flutter_cache to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

85501 Migrate dev/benchmarks/macrobenchmarks to null safety. (team, f: material design, cla: yes, a: null-safety)