Support attributes

[davispuh]

Currently ruby_ffi_generator doesn't support attributes, so code like this:

struct a {
  int b;
} __attribute__((aligned(4)));

Fails with:

lib/ffi_generator/generators/from_c_generator/generator.rb:322:in 'FFIGenerate::Generator#read_struct_or_union_declaration': unhandled exception
        from lib/ffi_generator/generators/from_c_generator/generator.rb:205:in 'FFIGenerate::Generator#read_declaration'
        from lib/ffi_generator/generators/from_c_generator/generator.rb:192:in 'block in FFIGenerate::Generator#declarations'
        from lib/ffi_generator/generators/from_c_generator/generator.rb:184:in 'Array#each'
        from lib/ffi_generator/generators/from_c_generator/generator.rb:184:in 'Enumerable#each_with_index'
        from lib/ffi_generator/generators/from_c_generator/generator.rb:184:in 'FFIGenerate::Generator#declarations'

This PR fixes that by adding attribute support.
Note that actually passing alignment requirements to FFI is not implemented and it will create regular struct like this

class A < FFI::Struct
  layout :b , :int
end

[Copilot]

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