Always enforce type-safety on sqlx queries

[qsantos]

Using non-macro sqlx::query does not enforce type safety. However, the macro seems to not allow for zero-copy decoding.

[qsantos]

There is currently no official zero-copy decoding in sqlx. However, switching to String for all the fields and using String everywhere reduces performance significantly.

In the current approach, row iteration actually performs no significant allocation and only checks that the strings are valid UTF-8:

Switching to the query_as! macro clearly shows that fields are being copied to new buffers in addition to being validated as UTF-8:

[qsantos]

So, this issue is basically blocked by launchbadge/sqlx#2661.