fix: Fix incorrect top-k by sorted column, fix head() returning extra rows

[nameexhaustion]

Fixes #20719

• top_k returns the wrong results if acting on sorted columns #20719

Fixes #20712

• head() gives more rows than the specified number of rows #20712

Fixes #20715

• ComputeError: input data is not sorted in group_by_dynamic #20715

Changelog

• Removes a descending parameter from SortOptions.limit - it is duplicated with the top-level descending config
• Fixes an issue where top_k on sorted data containing duplicates returned incorrect values (the duplicated rows were ignored):

pl.DataFrame({"a": [1, 2, 2]}).sort("a", descending=True).top_k(2, by="a")
# Before
shape: (2, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 2   │
│ 1   │
└─────┘
# After
shape: (2, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 2   │
│ 2   │
└─────┘

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.84%. Comparing base (1cd72ff) to head (acebf96).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...polars-core/src/chunked_array/ops/sort/arg_sort.rs	75.00%	1 Missing ⚠️
crates/polars-core/src/frame/column/mod.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20722      +/-   ##
==========================================
- Coverage   79.92%   79.84%   -0.08%     
==========================================
  Files        1559     1560       +1     
  Lines      221181   221396     +215     
  Branches     2530     2530              
==========================================
+ Hits       176774   176779       +5     
- Misses      43825    44035     +210     
  Partials      582      582              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[nameexhaustion]

Issue was this desc parameter, I've removed it