Add `benchmark` to gemspec dependencies for Ruby 3.4+ compatibility

[denysivanov]

When using rb_snowflake_client v1.5.0 with Ruby 3.4, the following warning is emitted on every load:

/lib/ruby_snowflake/client.rb:4: warning: benchmark was loaded from the standard library,
but will no longer be part of the default gems starting from Ruby 4.0.0.
You can add benchmark to your Gemfile or gemspec to silence this warning.
Also please contact the author of rb_snowflake_client-1.5.0 to request adding benchmark into its gemspec.

In Ruby 3.4, benchmark was promoted from a default gem to a bundled gem, which means it will no longer be available without an explicit dependency starting in Ruby 4.0.

Since client.rb requires benchmark at line 4, could you add it as a runtime dependency in the gemspec?

spec.add_dependency "benchmark"

This would silence the deprecation warning for all downstream users and ensure forward compatibility with Ruby 4.0.

Environment:

• Ruby 3.4.8
• rb_snowflake_client 1.5.0