Use hidden visibility for symbols for non-windows platforms

[svatasoiu]

this is to avoid polluting our .so's with visible symbols that might clash with other libraries when CSP is imported. default is basically public for gcc+clang, so this PR changes it to hidden (Windows does the opposite, the default is essentially publicly visible in the DLL symbol table)

reference: https://gcc.gnu.org/wiki/Visibility

[svatasoiu]

cannot reproduce the mac os build failures locally. I was able to successfully compile+run all tests on Python3.12 linux w/ clang 18.1.8, as well as clang 16.0.6 on mac os 13; but GH seems to be failing on clang 16.0.6 + OSX 12+14 builds with a mysterious error:

make: *** [test-py] Abort trap: 6

[svatasoiu]

Before:

$ nm -A -C -D --defined-only ./csp/lib/*.so | egrep -v "typeinfo|vtable|std::"  | awk -F':' '{print $1}' | uniq -c | sort -n
      8 ./csp/lib/_cspbasketlibimpl.so
      8 ./csp/lib/_csptestlibimpl.so
     44 ./csp/lib/_cspstatsimpl.so
     52 ./csp/lib/_cspnpstatsimpl.so
     73 ./csp/lib/_cspmathimpl.so
    168 ./csp/lib/_kafkaadapterimpl.so
    237 ./csp/lib/_cspbaselibimpl.so
    456 ./csp/lib/_cspimpl.so
    476 ./csp/lib/_csptypesimpl.so
    557 ./csp/lib/_parquetadapterimpl.so
    595 ./csp/lib/_websocketadapterimpl.so

After:

$ nm -A -C -D --defined-only ./csp/lib/*.so | egrep -v "typeinfo|vtable|std::"  | awk -F':' '{print $1}' | uniq -c | sort -n
      3 ./csp/lib/_cspbaselibimpl.so
      3 ./csp/lib/_cspbasketlibimpl.so
      3 ./csp/lib/_cspmathimpl.so
      3 ./csp/lib/_cspnpstatsimpl.so
      3 ./csp/lib/_cspstatsimpl.so
      3 ./csp/lib/_csptestlibimpl.so
     25 ./csp/lib/_cspimpl.so
     29 ./csp/lib/_kafkaadapterimpl.so
     33 ./csp/lib/_csptypesimpl.so
     40 ./csp/lib/_parquetadapterimpl.so
     86 ./csp/lib/_websocketadapterimpl.so

[robambalu]

Pls just make sure to squash commits when merging