Implicitly convert through string and integer in Time::at offset parsing

[lopopolo]

This doesn't look quite right.

[3.1.2] > class B; def to_str; 'B'; end; end
=> :to_str
[3.1.2] > Time.at(12, in: B.new)
=> 1970-01-01 02:00:12 +0200
[3.1.2] > class C; def to_str; raise 'crash'; end; end
=> :to_str
[3.1.2] > Time.at(12, in: C.new)
(irb):10:in `to_str': crash (RuntimeError)
        from <internal:timev>:274:in `at'
        from (irb):11:in `<main>'
        from /usr/local/var/rbenv/versions/3.1.2/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `load'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `<main>'
[3.1.2] > class D; def to_int; raise 'dint'; end; def to_str; raise 'dstr'; end; end
=> :to_str
[3.1.2] > Time.at(12, in: D.new)
(irb):12:in `to_str': dstr (RuntimeError)
        from <internal:timev>:274:in `at'
        from (irb):13:in `<main>'
        from /usr/local/var/rbenv/versions/3.1.2/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `load'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `<main>'

It looks like MRI prefers to implicitly convert through #to_str if it exists and otherwise will convert through #to_int. We can check for this by doing a Value::respond_to check.

Originally posted by @lopopolo in #1956 (comment)