feat(python)!: Remove serde functionality from pl.read_json and DataFrame.write_json

[stinodego]

Closes #14526

Changes

• pl.read_json no longer supports reading JSON files produced by DataFrame.serialize. Users should use pl.DataFrame.deserialize instead.
• DataFrame.write_json now only writes row-oriented JSON. The parameters row_oriented and pretty have been removed. Users should use DataFrame.serialize to serialize a DataFrame.

Example - write_json

Before:

>>> df = pl.DataFrame({"a": [1, 2], "b": [3.0, 4.0]})
>>> df.write_json()
'{"columns":[{"name":"a","datatype":"Int64","bit_settings":"","values":[1,2]},{"name":"b","datatype":"Float64","bit_settings":"","values":[3.0,4.0]}]}'

After:

>>> df.write_json()  # Same behavior as previously `df.write_json(row_oriented=True)`
'[{"a":1,"b":3.0},{"a":2,"b":4.0}]'

Example - read_json

Before:

>>> import io
>>> df_ser = '{"columns":[{"name":"a","datatype":"Int64","bit_settings":"","values":[1,2]},{"name":"b","datatype":"Float64","bit_settings":"","values":[3.0,4.0]}]}'
>>> pl.read_json(io.StringIO(df_ser))
shape: (2, 2)
┌─────┬─────┐
│ a   ┆ b   │
│ --- ┆ --- │
│ i64 ┆ f64 │
╞═════╪═════╡
│ 1   ┆ 3.0 │
│ 2   ┆ 4.0 │
└─────┴─────┘

After:

>>> pl.read_json(io.StringIO(df_ser))  # Format no longer supported: data is treated as a single row
shape: (1, 1)
┌─────────────────────────────────┐
│ columns                         │
│ ---                             │
│ list[struct[4]]                 │
╞═════════════════════════════════╡
│ [{"a","Int64","",[1.0, 2.0]}, … │
└─────────────────────────────────┘

Use instead:

>>> pl.DataFrame.deserialize(io.StringIO(df_ser))
shape: (2, 2)
┌─────┬─────┐
│ a   ┆ b   │
│ --- ┆ --- │
│ i64 ┆ f64 │
╞═════╪═════╡
│ 1   ┆ 3.0 │
│ 2   ┆ 4.0 │
└─────┴─────┘

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 81.50%. Comparing base (7cfa80a) to head (cc8acd6).
Report is 4 commits behind head on main.

Files	Patch %	Lines
py-polars/polars/dataframe/frame.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #16550    +/-   ##
========================================
  Coverage   81.50%   81.50%            
========================================
  Files        1412     1412            
  Lines      185133   185254   +121     
  Branches     2987     2994     +7     
========================================
+ Hits       150885   150990   +105     
- Misses      33730    33748    +18     
+ Partials      518      516     -2     

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