feat: Introduce (de-)serialization for schemas

[borchero]

Motivation

When serializing data frames to parquet, schema information beyond the simple polars schema is currently lost. However, persisting the schema alongside has multiple potential benefits:

• When reading the parquet file, schema information can be used to check whether the data adheres to the current schema without having to validate.
• Third-party tools can use advanced schema information to optimize operations

Since polars 1.30, the parquet writer supports writing file-level metadata. Naturally, dataframely schemas could be serialized as such.

This PR is the first step towards doing that: it introduces (de-)serialization for schemas from & to JSON.

Changes

• Introduce Schema.serialize and dy.deserialize_schema to serialize and de-serialize schemas to and from JSON

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (18481c1) to head (5873a7d).
Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%            
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  Files           39        41     +2     
  Lines         1954      2148   +194     
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+ Hits          1954      2148   +194     

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[AndreasAlbertQC]

Nice!