Dataframes chapter update to reflect the latest changes

[maxim-uvarov]

wip

[maxim-uvarov]

• updated benchmarks
• removed the part with loading benchmarks and left only group-by section
• updated reference texts accordingly
• renamed variables
• updated outputs of all the code chunks (and checked that they are executable)

I'm in the process of updating the markdown table with commands at the end of the chapter, but I will submit results a separate commit some other day.

There are still might be some typos, or incorrect explanations. I would be grateful if anybody could check them too.

[maxim-uvarov]

numd run dataframes.md --prepend-intermid "$env.config.footer_mode = 'never';
$env.config.table.header_on_separator = false; $env.config.table.mode = 'default'; $env.config.table.trim.methodology = wrapping; $env.config.table.abbreviated_row_count = 10000" --intermid-script `polars-eager.nu` --width 120 --echo --no-info | ansi strip | str replace -ar ' \d?\d?\d(ns|µs)' '' | save dataframes.md -f

[fdncred]

looking good. ready to land this?

[devyn]

0.94.0 is out now, but I'll hold off until @maxim-uvarov says this is good to go

[maxim-uvarov]

@devyn yes, please, merge it

[fdncred]

Thanks!