Release v2.0.21 (Fix `mapply`, Nested Data-Frame-Assignments, and CD Nestings)

What's Changed

• Attempt to fix the pat situation in the benchmark graphs by @Ellpeck in #958
• Include nested CDs based on nesting relationship by @EagleoutIce in #962
• feat-fix: function argument position forced by mapply by @EagleoutIce in #963
• feat-fix: nested data frame reassignments by @EagleoutIce in #964

Full Changelog: v2.0.20...v2.0.21