Interpret ? as a parameter only if .bind was called at least once

[slvrtrn]

Related to #154

Considering this query:

client
    .query("SELECT 1 FROM test WHERE a IN 'a?b'")
    .fetch_one::<u8>()
    .execute()
    .await?;

Currently, an unescaped ? is still considered a missing parameter; after the fix, the query should be written as:

client
    .query("SELECT 1 FROM test WHERE a IN 'a??b'")
    .fetch_one::<u8>()
    .execute()
    .await?;

This might be problematic if a query is pre-generated elsewhere (file, etc) and contains question marks, but we did not want to do any client-side binding.

[loyd]

The context: this crate uses custom parameters (implemented before CH started to support server-side parameters).
Now, server-side parameters can be used, as shown in #142 (comment) (not an ideal solution, but already possible). Users can use server-side parameters and don't realize that their queries can fail due to an extra ? in the query.

The idea here has a drawback: users will get an invalid query if they want to use ? but forget all .bind() calls. However, they will get a runtime error from CH in this case, so it's not a big difference.