FIX: Executemany String corruption on Unix systems + tests

[bewithgaurav]

Work Item / Issue Reference

AB#38479

GitHub Issue: #<ISSUE_NUMBER>

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Summary

Fix string handling in executemany batch operations on Unix systems

Issue:
executemany was corrupting string data on Unix/macOS due to encoding mismatch in batch parameter binding. Strings were either truncated or returned garbage data.

Root Cause:
In BindParameterArray function, std::wstring (UTF-32 on Unix) was directly copied to SQLWCHAR buffers (UTF-16) without proper encoding conversion, while single parameter binding in execute correctly used WStringToSQLWCHAR().

Fix:

• Added platform-specific string conversion in BindParameterArray for SQL_C_WCHAR case
• Unix: Use WStringToSQLWCHAR() for proper UTF-32 → UTF-16 conversion
• Windows: Keep existing direct copy (both are UTF-16)

Impact:

• All string data (including empty strings) now correctly preserved in executemany
• Eliminates data corruption and truncation on Unix platforms
• Maintains existing Windows behavior
• Consistent string handling between execute and executemany

[sumitmsft]

LEft a few comments.

The base branch was changed.