Fix (u)int8 implicit char conversion in stringstream

[kounelisagis]

This PR fixes the implicit character conversion that occurs when writing a (u)int8 value to a stringstream in the helper function std::string to_str(const T& value). By casting to (u)int32, we avoid this conversion.

This issue was discovered after encountering a UnicodeDecodeError when using operator<< in the TileDB-Py API on a TileDB Array schema that contained a (u)int8 attribute. Both a minimal TileDB-Py reproduction and the original issue involving TileDB-SOMA now work as expected.

[sc-61915]

---

TYPE: NO_HISTORY | BUG
DESC: Fix implicit character conversion in to_str by casting (u)int8 to (u)int32.

[teo-tsirpanis]

Thanks! Can you add a test in unit_parse_argument.cc? It doesn't exist currently.

[teo-tsirpanis]

Thanks!