Rename to $name$to_lowercase(), $name$to_uppercase(), $dt$total_seconds

[eitsupi]

There are some additional improvements that we could add here, in particular:

• feat(rust,python): add dedicated name namespace for operations that affect expression names polars#11973 for $name$to_lowercase() and $name$to_uppercase()
• depr(python,rust!): Rename dt.seconds to dt.total_seconds (likewise for days, hours, minutes, milliseconds, microseconds, and nanoseconds) polars#12179 (doesn't change anything on the rust side)

Originally posted by @etiennebacher in #515 (comment)