Build and compute the same on MSVC

[Force67]

rx main stopped compiling under MSVC after the STL removal (#66), and would have computed differently where it did.

• float math: std::sin(float) and friends had become ::sin(float). libstdc++'s <math.h> maps that to the float overload; MSVC's <math.h> has only the C double function, so it narrowed (errors) or silently ran the math in double. 1346 calls with all-float arguments, located by the compiler (float overloads that name themselves, compiled against a C-only <math.h>), now call the float function std::sin(float) calls (sinf, sqrtf, fabsf, ...); abs on floating values is fabs/fabsf (C's abs is the int one); 3-argument hypot, which C lacks, is rx::Hypot, step for step libstdc++'s. Linux is unchanged: GCC's front-end tree of every changed file resolves each rewritten call to the float overload before the change. A C-only <math.h> scan of rx now matches the libstdc++ build.
• window_sdl3.cc and path_tracer.cc had helper includes inside Linux-only / NRD-only #if blocks.
• script_string.h: HashStr and view() could never be constant expressions over base::StringRef (MSVC C3615), and a base::String was ambiguous to ScriptStringView under MSVC.
• AssetId: a defaulted operator<=> needs ; its four orderings are spelled out.
• tcp_stream.cc: under UNICODE gai_strerror is the wide variant (already broken before Replace the STL with equilibrium base and build without exceptions #66).
• world streaming: near is a <windows.h> macro; the band field and locals are renamed.
• mingw-shims gains WinSock2.h for zetanet.
• equilibrium bumped for fix(base): keep <windows.h> out of the lock and file headers equilibrium#22 (no <windows.h> through the lock and file headers).

Verified: a full MSVC build of anyvoxel with rx, zetanet, kinema (Force67/kinema#2) and libultragui links (anyvoxel CI windows-x64, via a temporary probe PR); ctest 153/153 under vkrun and all runtime/scenes captures pass rxdiff on Linux.