Fix: trilogy-libraries#11

The goals are:

  - Not raise any error that isn't a descendant of `Trilogy::Error`.
  - Have a clear distinction between transient network errors that may be retried, and invalid queries that shouldn't.

Unsolved issues (yet)

  - Trilogy calls `rb_syserr_fail_str` in a few places. Meaning it can still raise any of the `Errno::*` errors.
  - `handle_trilogy_error` raise all `TRILOGY_ERR` as `ProtocolError` which is a `ConnectionError`, but
     I'm not certain none of the possible errors could be considered client errors.

Instead of raising all ProtocolErrors as connection errors,
we use the SQL error code to determine the type of error to raise
when handling the Trilogy error in the Ruby bindings.

The mapping of error codes to error classes was taken from the mysql2
implementation: https://github.com/brianmario/mysql2/blob/master/lib/mysql2/error.rb#L13-L27

Note that we don't need to care about the 2xxx errors because those
are raised by the libmysql client, which Trilogy doesn't deal with.

Co-authored-by: Jean Boussier <jean.boussier@shopify.com>