bone_sse: replace matMul/ftol/vec3SqMag with pure Zig, fix visual artifacts

Root cause of billboard visual artifacts: callVec3SqMag used inline asm
to call game's x87 vec3SqMag (0x4549F0) with fstps to capture ST0.
With SSE2 codegen, the x87/SSE state interaction caused corrupted float
values in billboard bone matrices (mat[0][2] wildly wrong).

Replaced with pure Zig: x*x + y*y + z*z — no x87, no inline asm.

Also replaced:
- matMul (0x74A7C0): pure Zig f64 scalar matmul, no alignment needs
- callFtol (0x40A2B0): f64 intermediate + @intFromFloat (cvttsd2si)

Architecture: bone_sse.zig is REF code compiled with SSE2, called as
cdecl from thiscall wrapper in transform44.zig (cross-object to prevent
LLVM inlining AND ESP alignment into thiscall frame).

A/B: other hooks gated behind AB_OTHER_HOOKS=false for isolated testing.

build.zig

@@ -67,7 +67,7 @@ pub fn build(b: *std.Build) void {
         .cpu_arch = .x86,
         .os_tag = .windows,
         .abi = .msvc,
-        .cpu_features_add = std.Target.x86.featureSet(&.{ .sse, .sse2, .sse3, .sse4_1, .fma, .avx }),
+        .cpu_features_add = std.Target.x86.featureSet(&.{ .sse, .sse2 }),
     });
     const bone_sse_obj = b.addObject(.{
         .name = "bone_sse",