Variable can't contain backslash

This is an example code.
```js
const text = 'abc\\';
await client.execute('insert into users(name) values(?)', [text]);
```
This is a result of the query string.
```sql
insert into users(name) values("abc\")
```
So, it will throw an error.

Start by reproducing the provided JavaScript example against the Deno MySQL driver, then trace the parameter escaping that produces the SQL shown in the issue. Done means a value containing a trailing backslash inserts successfully without an SQL error, with coverage for this case if the project’s existing tests provide a suitable place.

Written by the indexing model from the issue text.