tests: add DML analog for Issue #161 (no stored procedure)

The existing Issue161_SLongToVarcharViaStoredProcedure test is skipped
on Firebird 6 because of a pre-existing FB6 parameterized-SP
regression (SKIP_ON_FIREBIRD6), which means the fix is not exercised
on the FB6 matrix jobs.

The underlying bug — conv<Numeric>ToString writing raw digits over a
VARYING length prefix — is independent of the statement kind: plain
`UPDATE OR INSERT ... VALUES (?, ?) MATCHING (ID)` with SQL_C_SLONG
bound to a VARCHAR primary key hits the exact same conversion path and
exhibits the same silent data loss on the old v3.0.1.21 driver (500
rows sent, 11 stored, one with embedded NUL byte).

Add a DML-only analog of the SP test.  It runs on every server
version in the matrix including FB 6, closing the gap left by the
SP test's SKIP_ON_FIREBIRD6.

Author: fdcastel

tests/test_param_conversions.cpp

@@ -385,6 +385,89 @@ TEST_F(ParamConversionsTest, Issue161_SLongToVarcharViaStoredProcedure) {
     ReallocStmt();
 }
 
+// Same scenario as Issue161_SLongToVarcharViaStoredProcedure, but without a
+// stored procedure — `UPDATE OR INSERT ... VALUES (?, ?) MATCHING (ID)` with
+// SQL_C_SLONG bound to a VARCHAR primary key.  The issue body claimed plain
+// DML was unaffected, but empirical testing against the old v3.0.1.21 driver
+// shows the identical silent data loss (500 rows sent, 11 stored, one with
+// embedded NUL byte) — the bug lives entirely in the conv*ToString path and
+// does not care about the statement kind.  This test exercises the same
+// driver fix on every server version in the matrix (including FB 6, where
+// plain DML does not trip the SKIP_ON_FIREBIRD6 parameterized-SP regression).
+TEST_F(ParamConversionsTest, Issue161_SLongToVarcharViaDml) {
+    ExecIgnoreError("DROP TABLE ODBC_ISSUE161_T");
+    Commit();
+    ReallocStmt();
+
+    ExecDirect("CREATE TABLE ODBC_ISSUE161_T ("
+               "ID VARCHAR(20) NOT NULL PRIMARY KEY, "
+               "NAME VARCHAR(100))");
+    Commit();
+    ReallocStmt();
+
+    constexpr int kRowCount = 500;
+    SQLINTEGER idVal = 0;
+    SQLLEN idInd = sizeof(idVal);
+    SQLCHAR nameBuf[32] = {};
+    SQLLEN nameInd = SQL_NTS;
+
+    SQLRETURN ret = SQLPrepare(hStmt,
+        (SQLCHAR*)"UPDATE OR INSERT INTO ODBC_ISSUE161_T (ID, NAME) "
+                  "VALUES (?, ?) MATCHING (ID)", SQL_NTS);
+    ASSERT_TRUE(SQL_SUCCEEDED(ret))
+        << "SQLPrepare failed: " << GetOdbcError(SQL_HANDLE_STMT, hStmt);
+
+    ret = SQLBindParameter(hStmt, 1, SQL_PARAM_INPUT,
+        SQL_C_SLONG, SQL_INTEGER, 0, 0, &idVal, sizeof(idVal), &idInd);
+    ASSERT_TRUE(SQL_SUCCEEDED(ret))
+        << "SQLBindParameter(1) failed: " << GetOdbcError(SQL_HANDLE_STMT, hStmt);
+
+    ret = SQLBindParameter(hStmt, 2, SQL_PARAM_INPUT,
+        SQL_C_CHAR, SQL_VARCHAR, 100, 0, nameBuf, sizeof(nameBuf), &nameInd);
+    ASSERT_TRUE(SQL_SUCCEEDED(ret))
+        << "SQLBindParameter(2) failed: " << GetOdbcError(SQL_HANDLE_STMT, hStmt);
+
+    for (int i = 1; i <= kRowCount; ++i) {
+        idVal = i;
+        snprintf((char*)nameBuf, sizeof(nameBuf), "name-%d", i);
+        ret = SQLExecute(hStmt);
+        ASSERT_TRUE(SQL_SUCCEEDED(ret))
+            << "SQLExecute failed on row " << i << ": "
+            << GetOdbcError(SQL_HANDLE_STMT, hStmt);
+    }
+    Commit();
+    ReallocStmt();
+
+    ExecDirect("SELECT COUNT(*), MIN(CAST(ID AS INTEGER)), MAX(CAST(ID AS INTEGER)) "
+               "FROM ODBC_ISSUE161_T");
+    ret = SQLFetch(hStmt);
+    ASSERT_TRUE(SQL_SUCCEEDED(ret)) << "SQLFetch on aggregate failed";
+
+    SQLINTEGER cnt = 0, minId = 0, maxId = 0;
+    SQLLEN ind = 0;
+    SQLGetData(hStmt, 1, SQL_C_SLONG, &cnt, sizeof(cnt), &ind);
+    SQLGetData(hStmt, 2, SQL_C_SLONG, &minId, sizeof(minId), &ind);
+    SQLGetData(hStmt, 3, SQL_C_SLONG, &maxId, sizeof(maxId), &ind);
+    SQLCloseCursor(hStmt);
+
+    EXPECT_EQ(cnt, kRowCount);
+    EXPECT_EQ(minId, 1);
+    EXPECT_EQ(maxId, kRowCount);
+
+    ExecDirect("SELECT COUNT(*) FROM ODBC_ISSUE161_T "
+               "WHERE POSITION(_OCTETS x'00' IN ID) > 0");
+    ret = SQLFetch(hStmt);
+    ASSERT_TRUE(SQL_SUCCEEDED(ret)) << "SQLFetch on NUL check failed";
+    SQLINTEGER nulCount = -1;
+    SQLGetData(hStmt, 1, SQL_C_SLONG, &nulCount, sizeof(nulCount), &ind);
+    SQLCloseCursor(hStmt);
+    EXPECT_EQ(nulCount, 0) << "rows with embedded NUL bytes were stored";
+
+    ExecIgnoreError("DROP TABLE ODBC_ISSUE161_T");
+    Commit();
+    ReallocStmt();
+}
+
 // ===== Already-covered round-trip tests from test_data_types.cpp =====
 // (IntegerParamInsertAndSelect, VarcharParamInsertAndSelect,
 //  DoubleParamInsertAndSelect, DateParamInsertAndSelect,