Ractor support

Hello maintainers,

Is there any interest or planned change to add support to this gem for use within a Ruby 3 Ractor?

Currently, constructing a database instance is failing with the error message introduced into this Ruby commit. I have collected this stacktrace:

~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/sqlite3-1.4.2/lib/sqlite3/database.rb:89:in `open_v2': ractor unsafe method called from not main ractor (Ractor::UnsafeError)
        from ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/sqlite3-1.4.2/lib/sqlite3/database.rb:89:in `initialize'
        ...

It can be reproduced by:

sqlite_ractor = Ractor.new do
    db = SQLite3::Database.open "xyz.db"
end
puts sqlite_ractor.take

The Ruby commit message justifies the error because:

C extensions can violate the ractor-safety

However, this gem doesn't appear to store references to Ruby objects that might be accessed across Ractors / invalidly shared, so perhaps its C extensions can be marked as Ractor-safe?

Start with lib/sqlite3/database.rb:89 and run the Ractor reproduction in the issue under Ruby 3. Trace the C-extension path involved in opening the database and determine what Ractor support requires. Done means the example can construct and use the database from a non-main Ractor without Ractor::UnsafeError.