Go 1.27.3 math, patched for lys-lib

A copy of the functions of Go 1.27.3's standard math package whose results depend on the architecture (BSD 3-Clause, LICENSE): Sin, Cos, Sincos, Tan, Atan, Atan2, Asin, Acos, Exp, Exp2, Log, Log2, Log10, Pow, Cbrt, Hypot, Erf and Erfc, imported as github.com/stubbedev/lys-lib/third_party/gomath. Every lys package calls these instead of math's, which .golangci.yml enforces. Sqrt, Floor, Abs, Mod and the rest of math are exact, so they stay in math.

Why the standard library is not enough

math's results differ between architectures in two ways:

• Its portable code is ordinary Go, and on arm64 the compiler fuses its x*y + z into FMAs. Go's own tests allow for that with a tolerance, so math.Sin on arm64 is not math.Sin on amd64.
• Exp is assembly on amd64 and on arm64, and Log and Hypot on amd64. amd64's Exp also picks an FMA path at run time from the CPU, so its results differ between x86 CPUs too. Pow and Erfc call Exp.

Patches

Portable code only

The haveArch* branches to assembly are gone, and math's exact helpers are called through math.

Products round the same on every architecture

As in third_party/rasterx, each product that reaches an addition or a subtraction is converted first. On amd64, against math: 20000 inputs per function gave the same bits for Sin, Cos, Tan, Atan, Asin, Acos, Exp2, Log, Log2, Log10, Cbrt and Hypot. Exp differs on 16% of inputs, Pow on 12% and Erfc on 7%, by the last bits, because the assembly Exp is gone. Pinned by gomath_test.go, whose single table of hashes holds on every architecture.