API: add ignore index keyword to dropna() and other similar functions

API: add ignore index keyword to dropna() and other similar functions: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I have noticed a lot of dataframe reshaping functions acquiring the ignore index keyword. (e.g. 30114). I think df.dropna() is a good candidate…

The task

I have noticed a lot of dataframe reshaping functions acquiring the `ignore_index` keyword. (e.g. #30114). I think `df.dropna()` is a good candidate for this keyword, as are any other functions which change the index from being a consecutive sequence of integers

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.