math is a core, widely-imported stdlib package; greening it (and math/bits, which unblocked it)
is a major step in the Phase 3 full-conversion compile drive.

This session greened 9 full-conversion packages — unicode, internal/trace/event, unicode/utf16,
internal/platform, image/color, runtime/internal/sys, runtime/internal/math, math/bits, math —
via 19 behaviorally-tested converter/generator fixes. The dominant theme was comprehensive
untyped-constant typing (append / shift / arithmetic / comparison / BigInteger / bitwise /
float64-default / native-int const), plus shadowing (type-switch guard, nested-var, partial
redeclaration), namespace-collision qualification, composite self-qualification, and
relational-pattern guards.