Metadata statement cleanup depends on closeOnCompletion behavior that #86 proposes to change #119

#91 closes metadata statements through executeMetadataQuery. The statement closes only because closeOnCompletion auto-closes it when the result set closes. #86 proposes to match sqlite-jdbc, which only tracks that flag.

LibsqlResultSet already has a closeStatementOnClose flag, but no caller sets it to true, so it is dead code.

If #86 is fixed the sqlite-jdbc way, the leak returns for every metadata method. Only MetadataLeakTest would notice, and it exercises getTables only.

Expected:

• Build metadata result sets with closeStatementOnClose = true.
• Extend the leak-count test to every metadata method that opens a statement.
• Land this before the fix for closeOnCompletion auto-closes on ResultSet.close; xerial only tracks the flag #86.