Add support for PostgreSQL CREATE RULE

[LucaCappelletti94]

The parser does not recognize CREATE RULE at all, so any PostgreSQL schema that defines rewrite rules fails to parse. pg_dump emits rules whenever a schema has them, which makes complete schema dumps unparseable.

Documentation: https://www.postgresql.org/docs/current/sql-createrule.html

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.85106% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.09%. Comparing base (bfc7d38) to head (00a9885).

Files with missing lines	Patch %	Lines
src/parser/mod.rs	76.78%	4 Missing and 9 partials ⚠️
src/ast/ddl.rs	88.88%	1 Missing and 3 partials ⚠️
src/ast/spans.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2433      +/-   ##
==========================================
- Coverage   81.09%   81.09%   -0.01%     
==========================================
  Files          42       42              
  Lines       33682    33776      +94     
  Branches    33682    33776      +94     
==========================================
+ Hits        27316    27392      +76     
- Misses       2796     2802       +6     
- Partials     3570     3582      +12     

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