Add transform_row and scalar_parser documentation and make them easier to use

[kmcq]

Purpose

As a follow up to #117, we wanted to document the new capabilities in the README and to make it a bit easier to use the new scalar_parser configuration of queries.

Overview

• Add an attr_accessor for scalar_parser to Query
• Pass this along in column_value_parsers
• Fix an issue where the shorthand used in Query#transform_rows was incorrect (sorry!)
• Add an example of using transform_row and scalar_parser to the README.

@fionaochs paired on this with me 🎉

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary

[kmcq]

👋 I noticed that we didn't increase the version number for the last change I did:

trino-client-ruby/lib/trino/client/version.rb

Line 18 in e14251c

VERSION = "2.0.1"

Do you want me to bump that to 2.1.1 in this PR?

[yuokada]

@kmcq Thanks. I forgot to do git-push.

d1078c0

[takezoe]

scalar_parser is replaceable but looks like ColumnValueParser won't be recreated once instanciated even if scalar_parser is replaced.

client.query("select * from sys.node") do |q|
  q.each_row {|row|
    q.scalar_parser = scalar_parser1
    p q.transform_row(row)

    # Expect scalar_parser2 is used but scalar_parser1 is actually used?
    q.scalar_parser = scalar_parser2
    p q.transform_row(row)
  }
end

I know this example is artificial but behavior is counterintuitive.

[kmcq]

@takezoe great point! Agreed that this likely wouldn't happen, but that it could be a problem for someone who needs it. I have updated this in 035679d while keeping the memoization intact. Now the scalar_parser can be changed and I updated the tests to show this.

[takezoe]

Looks very good. Thank you!

[takezoe]

LGTM

[yuokada]

@kmcq We released v2.2.0. Thanks for your contribution.
https://rubygems.org/gems/trino-client/versions/2.2.0
https://github.com/treasure-data/trino-client-ruby/releases/tag/v2.2.0

[kmcq]

Thanks @yuokada! And thanks again for the reviews @takezoe. We're now using 2.2.0 with no modifications 🎉 I hope these features help others as well