MSVC compiler warnings

[rdmark]

MSVC in the GitHub windows-latest runner throws a handful of warnings which it worth looking closer at

2026-01-09T18:54:38.6166578Z ninja: Entering directory `D:/a/bstring/bstring/build'
2026-01-09T18:54:38.6168464Z [1/3] "C:\Strawberry\c\bin\ccache.EXE" "cl" "-Ibstring\bstring-1.dll.p" "-Ibstring" "-I..\bstring" "-I." "-I.." "/MDd" "/nologo" "/showIncludes" "/utf-8" "/W4" "/Od" "/Z7" "/we4431" "/w14826" "/Fdbstring\bstring-1.dll.p\bstraux.c.pdb" /Fobstring/bstring-1.dll.p/bstraux.c.obj "/c" ../bstring/bstraux.c
2026-01-09T18:54:38.6170410Z ../bstring/bstraux.c(237): warning C4100: 'parm': unreferenced parameter
2026-01-09T18:54:38.6171654Z ../bstring/bstraux.c(236): warning C4100: 'nelem': unreferenced parameter
2026-01-09T18:54:38.6172538Z ../bstring/bstraux.c(235): warning C4100: 'elsize': unreferenced parameter
2026-01-09T18:54:38.6173738Z ../bstring/bstraux.c(234): warning C4100: 'buff': unreferenced parameter
2026-01-09T18:54:38.6174754Z ../bstring/bstraux.c(1007): warning C4245: '=': conversion from 'int' to 'size_t', signed/unsigned mismatch
2026-01-09T18:54:38.6583104Z [2/3] "C:\Strawberry\c\bin\ccache.EXE" "cl" "-Ibstring\bstring-1.dll.p" "-Ibstring" "-I..\bstring" "-I." "-I.." "/MDd" "/nologo" "/showIncludes" "/utf-8" "/W4" "/Od" "/Z7" "/we4431" "/w14826" "/Fdbstring\bstring-1.dll.p\bstrlib.c.pdb" /Fobstring/bstring-1.dll.p/bstrlib.c.obj "/c" ../bstring/bstrlib.c
2026-01-09T18:54:38.7181957Z [3/3] "link"  /MACHINE:x64 /OUT:bstring/bstring-1.dll bstring/bstring-1.dll.p/bstraux.c.obj bstring/bstring-1.dll.p/bstrlib.c.obj "/release" "/nologo" "/DEBUG" "/PDB:bstring\bstring-1.pdb" "/DLL" "/IMPLIB:bstring\bstring.lib" "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib" "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "comdlg32.lib" "advapi32.lib"
2026-01-09T18:54:38.7203403Z INFO: autodetecting backend as ninja
2026-01-09T18:54:38.7204724Z INFO: calculating backend command to run: C:\hostedtoolcache\windows\Python\3.14.2\x64\Scripts\ninja.EXE -C D:/a/bstring/bstring/build -v