refactor: Move IO specifics out of Schema, Collection

[AndreasAlbertQC]

Motivation

The current implementation of parquet-based storage is strongly coupled to the implementation of the Schema and Collection classes. This makes it hard to reuse parts of the logic that would also be useful for other future storage backends. To prepare the implementation of such future storage backends, this PR refactors the current logic to introduce a clearer interface for storage backends.

Changes

• Introduced the notion of a StorageBackend, i.e. a piece of code encapsulating a way of storing data and metadata.
• Refactored the parquet storage logic to use the StorageBackend interface

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.88%. Comparing base (fbf08c8) to head (292a8b6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #109      +/-   ##
===========================================
- Coverage   100.00%   99.88%   -0.12%     
===========================================
  Files           42       42              
  Lines         2443     2525      +82     
===========================================
+ Hits          2443     2522      +79     
- Misses           0        3       +3     

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