Inconsistent run-time library usage for locale handling breaks GPU code generation on some systems. #2351

Several GPU code paths format float constants with std::to_string(), which follows the C runtime locale (LC_NUMERIC). All other float formatting in OCIO follows the C++ global locale, for example via std::ostringstream. These are independent settings, so on comma-decimal systems (e.g. fr_FR, sv_SE) the two mechanisms can produce different decimal separators in the same shader. The affected call sites emit literals such as 100 000000 instead of 100.0, while neighboring constants from getFloatString() remain correct. The resulting GLSL/HLSL fails to compile or produces incorrect output.

This is most visible with ACES 2.x fixed-function GPU paths (gamut compress / tone scale), but the same pattern exists in grading-tone GPU code.

Affected call sites (12 float std::to_string calls across 7 lines, 2 files):

ops/fixedfunction/FixedFunctionOpGPU.cpp

• _Add_Focus_Gain_func (line 947)
• _Add_Compress_Gamut_func (line 1187)
• _Add_Gamut_Compress_Inv_Shader (line 1269)

ops/gradingtone/GradingToneOpGPU.cpp

• Add_MidsPre_Shader (line 304)
• Add_SContrastTopPre_Shader (lines 1249, 1260)
• Add_SContrastBottomPre_Shader (line 1300)

Suggested fix: Replace std::to_string(float) with getFloatString(), or route through the existing FloatToString() helpers in ParseUtils.cpp.