Driver registry

[krlmlr]

This PR does many things:

• Cleanup (before commit "Efficient lookup")
• Fix how GC is prevented for metadata for registered Arrow tables (was: attributes, now: part of the std::unordered_map<> in C++; before commit "Store config with driver object"
• Pick up all arguments passed to duckdb() in dbConnect(), and vice versa (before commit "path_normalize")
• Implement driver registry, closes Reuse database object #123.
• Tests

With this change, each database file is opened only once, by the call to duckdb() . The database file is closed when the last connection is closed correctly with dbDisconnect(), or when it is garbage-collected (with a warning). The connection still must be closed with dbDisconnect(), but the shutdown argument that was necessary before is now meaningless.

• Add tests
• Describe
• Check consistency of config and readonly objects
• revdepcheck

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.35484% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 86.28%. Comparing base (210db9b) to head (321cece).

❗ Current head 321cece differs from pull request most recent head 2cab803. Consider uploading reports for the commit 2cab803 to get more accurate results

Files	Patch %	Lines
src/database.cpp	78.57%	3 Missing ⚠️
R/Driver.R	92.59%	2 Missing ⚠️
src/connection.cpp	80.00%	1 Missing ⚠️
src/include/rapi.hpp	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
+ Coverage   85.87%   86.28%   +0.41%     
==========================================
  Files         107      107              
  Lines        3639     3712      +73     
==========================================
+ Hits         3125     3203      +78     
+ Misses        514      509       -5     

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[krlmlr]

Merging now to get binaries from r-universe. Highly appreciate your review!