fix(python, rust): Validate schema in melt

[edavisau]

Fixes #13493

This assumes that

1. There are no duplicate column names among id_vars and value_vars
2. All column names in id_vars and value_vars exist in the schema

Condition 1 prevents invalid dataframes from being constructed as follows

import polars as pl

pl.DataFrame([pl.Series("a", [1,2,3])]).melt(id_vars=["a", "a", "a", "a"], value_vars=["a", "a"])

# shape: (6, 6)
# ┌─────┬─────┬─────┬─────┬──────────┬───────┐
# │ a   ┆ a   ┆ a   ┆ a   ┆ variable ┆ value │
# │ --- ┆ --- ┆ --- ┆ --- ┆ ---      ┆ ---   │
# │ i64 ┆ i64 ┆ i64 ┆ i64 ┆ str      ┆ i64   │
# ╞═════╪═════╪═════╪═════╪══════════╪═══════╡
# │ 1   ┆ 1   ┆ 1   ┆ 1   ┆ a        ┆ 1     │
# │ 2   ┆ 2   ┆ 2   ┆ 2   ┆ a        ┆ 2     │
# │ 3   ┆ 3   ┆ 3   ┆ 3   ┆ a        ┆ 3     │
# │ 1   ┆ 1   ┆ 1   ┆ 1   ┆ a        ┆ 1     │
# │ 2   ┆ 2   ┆ 2   ┆ 2   ┆ a        ┆ 2     │
# │ 3   ┆ 3   ┆ 3   ┆ 3   ┆ a        ┆ 3     │
# └─────┴─────┴─────┴─────┴──────────┴───────┘

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.26%. Comparing base (92902e6) to head (6c86d88).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15514   +/-   ##
=======================================
  Coverage   81.25%   81.26%           
=======================================
  Files        1371     1371           
  Lines      175772   175785   +13     
  Branches     2531     2531           
=======================================
+ Hits       142831   142848   +17     
+ Misses      32464    32462    -2     
+ Partials      477      475    -2     

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

[codspeed-hq]

CodSpeed Performance Report

Merging #15514 will not alter performance

_{Comparing edavisau:melt-panic (6c86d88) with main (92902e6)}

Summary

✅ 21 untouched benchmarks

[edavisau]

Not sure why the unit tests failed in the previous commit, passing now. Though CodSpeed is now failing 😮