Enable MySQL "LOAD DATA LOCAL" with url option

[TheLQ]

Enable LOAD DATA LOCAL in batch_execute. mysqlclient handles all the IO. I'm inserting 30 million rows significantly faster now.

With native Diesel support, the mysql and postgres versions get complicated quickly. Also LOAD DATA isn't supported in transactions. This option is enough for me to do it when rarely needed.

Example

fn main() {
    let url = "mysql://u:p@localhost/db?local_infile";
    let conn = &mut MysqlConnection::establish(url).unwrap();
    conn.batch_execute(
        "CREATE TEMPORARY TABLE fast_table (\
        id INT NOT NULL PRIMARY KEY,\
        value VARCHAR(20) NOT NULL\
        )",
    )
        .unwrap();

    let load_path = Path::new("mysql-rows.dat");
    write_rows_file(&load_path);
    load_rows_file(conn, &load_path);
}

const ROW_SEP: u8 = 0x1e;
const COL_SEP: u8 = 0x1f;
fn write_rows_file(path: &Path) -> () {
    let mut out_file = File::create(path).unwrap();
    for row in 0..10 {
        let something = "something";
        write!(out_file, "{row}{COL_SEP}{something}{ROW_SEP}").unwrap();
    }
}

fn load_rows_file(conn: &mut MysqlConnection, path: &Path) {
    conn.batch_execute(&format!(
        "LOAD DATA LOCAL INFILE '{}' \
        INTO TABLE `fast_table` \
        FIELDS TERMINATED BY '{COL_SEP}' \
        LINES TERMINATED BY '{ROW_SEP}' \
        (id, value)",
        path.display()
    ))
        .unwrap()
}

[JohnTitor]

Also I'd tweak ConnectionOptions and add tests.

[JohnTitor]

local_infile should take binary value so we need handle it as well: https://dev.mysql.com/doc/refman/8.4/en/mysql-command-options.html#option_mysql_local-infile

[TheLQ]

Initially used mysqlclient's default compiled flag (usually disabled) or explicit enable.

To have explicit enable and disable we need to use mysql_option instead.
Docs for MYSQL_OPT_LOCAL_INFILE https://dev.mysql.com/doc/c-api/9.5/en/mysql-options.html

Added parsing unit test. Example above was successful too.

[TheLQ]

Rebased after #4972 so tests pass. Also fixed the doc comment.