Add support for SQL query caching

[JakobGM]

TODO

• Rename QueryCacher to QuerySource.
• Add documentation tutorial for using this functionality.
• Use XDG_CACHE_HOME for default cache location.
• Rename sql_to_arrow to query_handler.
• Allow QuerySource.query() to execute a SQL query string directly if provided.
• Rename QueryCache to QuerySource since caching is not necessarily involved.
• Add support for hashing other parameter passed to the query handler (left as future TODO).
• Add support for writing cache files to other locations, such as Google CloudStorage (left as future TODO).
• Rename patito.QuerySource to patito.Database, move everything DuckDB-related into patito.duckdb.

[codecov-commenter]

Codecov Report

Merging #51 (6dff76d) into main (164ebed) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              main       #51    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files            7         9     +2     
  Lines          956      1103   +147     
  Branches       224       242    +18     
==========================================
+ Hits           956      1103   +147     

Impacted Files	Coverage Δ
src/patito/duckdb.py	100.00% <ø> (ø)
src/patito/sql.py	100.00% <ø> (ø)
src/patito/validators.py	100.00% <ø> (ø)
src/patito/__init__.py	100.00% <100.00%> (ø)
src/patito/database.py	100.00% <100.00%> (ø)
src/patito/xdg.py	100.00% <100.00%> (ø)

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