feat: New df_to_parquet() to write to Parquet, new convenience df_from_csv(), duckdb_df_from_csv(), df_from_parquet() and duckdb_df_from_parquet()

[krlmlr]

Closes #87. Closes #89. Closes #96.

[eitsupi]

How about use _read_ and _write_ instead of _from_ and _to_?

[krlmlr]

df_read_file() ? It's not strictly reading -- the reading only happens during materialization. Keeping it now as is, we can revisit later.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 9.75%. Comparing base (9e952d7) to head (eb9e6d9).

❗ Current head eb9e6d9 differs from pull request most recent head e97b432. Consider uploading reports for the commit e97b432 to get more accurate results

Files	Patch %	Lines
R/io-csv.R	50.00%	2 Missing ⚠️
R/io-parquet.R	71.42%	2 Missing ⚠️
R/io.R	50.00%	2 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff            @@
##            main    #128      +/-   ##
========================================
+ Coverage   9.66%   9.75%   +0.09%     
========================================
  Files        127     129       +2     
  Lines      22633   22646      +13     
========================================
+ Hits        2187    2209      +22     
+ Misses     20446   20437       -9     

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