fix: infer types for untyped query binds

[zhaitz]

• queries like Singer.where("first_name = ?", "Alice") on Rails 8.1 (and similar Arel.sql queries) send an untyped string into the adapter which gets declared as int64
• so, update to_types_and_params to infer the correct Spanner types for these values
• uses an allowlist to preserve the existing behavior for arrays and other unsupported types

[gemini-code-assist]

Code Review

This pull request updates the Spanner adapter to dynamically resolve types for untyped bind values based on their Ruby class, falling back to :INT64 for unsupported types, and adds corresponding unit tests. The review feedback identifies a critical issue where ActiveSupport::TimeWithZone is not handled by the new untyped_bind_type method, which would cause it to fall back to :INT64 and lead to query errors. A code suggestion is provided to explicitly handle ActiveSupport::TimeWithZone.

[gemini-code-assist]

In Rails, timezone-aware attributes and queries (such as Time.zone.now) return ActiveSupport::TimeWithZone objects rather than standard Ruby Time objects. Since ActiveSupport::TimeWithZone does not inherit from Time or Date, it will not match the case statement in untyped_bind_type and will fall back to :INT64. This will cause Spanner type mismatch errors or serialization failures when executing queries with untyped timezone-aware time binds.

We should explicitly handle ActiveSupport::TimeWithZone if it is defined.

        def untyped_bind_type value
          if value.is_a?(::String) || value.is_a?(::Float) || value.is_a?(::BigDecimal) || value.is_a?(::Time) || value.is_a?(::Date) || (defined?(ActiveSupport::TimeWithZone) && value.is_a?(ActiveSupport::TimeWithZone))
            Google::Cloud::Spanner::Convert.field_for_object value
          else
            # Preserve the existing fallback for nil and unsupported values.
            :INT64
          end
        end

[zhaitz]

ActiveSupport::TimeWithZone overrides is_a? so this works: https://github.com/rails/rails/blob/3989ebf3473d71e4ceca28154b0b57b5bf22db24/activesupport/lib/active_support/time_with_zone.rb#L511

but can add a test to demonstrate that