This commit uses OpenStruct only if available because of the following reasons:

- Starting from Ruby 3.4.0dev, Using `ostruct` raises the following warning.
> ostruct was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.5.0. Add ostruct to your Gemfile or gemspec.

- And when the warning category is `:performance` it also raises this warning.
> "OpenStruct use is discouraged for performance reasons

Refer to
https://bugs.ruby-lang.org/issues/20309
ruby/ruby#10428
ruby/ostruct#56
Fix #561

This PR adds `ostruct` to runtime dependency to suppress the following warning:

```console
$ ruby -v
ruby 3.4.0dev (2024-04-19T07:33:16Z master 7951b349ab) [x86_64-darwin23]
$ cd path/to/rubocop
$ bundle exec rake
/Users/koic/.rbenv/versions/3.4-dev/lib/ruby/gems/3.4.0+0/gems/yard-0.9.36/lib/yard/templates/template_options.rb:2:
warning: ostruct was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.5.0. Add ostruct to your Gemfile or gemspec.
```

This change is aimed at Ruby 3.5 and will start showing warnings from Ruby 3.4:
ruby/ruby#10428

To maintain the following behavior, the dependency will be added in the gemspec to resolve this.
https://github.com/lsegal/yard/blob/v0.9.36/lib/yard/templates/template_options.rb#L32-L34

requiring ostruct is introduced at rspec@5cd41d3 and
removed using OpenStruct at rspec@d7e4033 .
ostruct was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.5.0.
Related https://bugs.ruby-lang.org/issues/20309 ruby/ruby#10428

requiring ostruct is introduced at rspec@5cd41d3 and
removed using OpenStruct at rspec@d7e4033 .
ostruct was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.5.0.
Related https://bugs.ruby-lang.org/issues/20309 ruby/ruby#10428

Starting in Ruby 3.5, `pstore` and `ostruct` will not be bundled with
Ruby's default gems, and will need to be added as explicit
dependencies. The deprecation warnings merged into 3.4 for
[pstore][pstore] and [ostruct][ostruct] and then backported for the
[release of 3.3.5][3.3.5]

[pstore]: ruby/ruby#10430
[ostruct]: ruby/ruby#10428
[3.3.5]: ruby/ruby#11420

This commit bumps the required Rake version to suppress the following warnings:

```ruby
$ ruby -v
ruby 3.4.0dev (2024-10-21T16:48:53Z master 5131fb5dbe) +PRISM [x86_64-linux]
$ bundle exec rake 2>&1 |grep -i ostruct
ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
/home/yahonda/.rbenv/versions/trunk/lib/ruby/gems/3.4.0+0/gems/rake-12.3.3/lib/rake/rake_test_loader.rb:2: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
./home/yahonda/src/github.com/rails/sprockets/lib/rake/sprocketstask.rb:2: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
```

- Rake v13.2.0 does not depend on OpenStruct
https://github.com/ruby/rake/releases/tag/v13.2.0
ruby/rake#545

- Ruby 3.4.0dev emits OpenStruct warnings
https://bugs.ruby-lang.org/issues/20309
ruby/ruby#10428

This commit bumps the required Rake version to suppress the following warnings:

```ruby
$ ruby -v
ruby 3.4.0dev (2024-10-21T16:48:53Z master 5131fb5dbe) +PRISM [x86_64-linux]
$ bundle exec rake 2>&1 |grep -i ostruct
ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
/home/yahonda/.rbenv/versions/trunk/lib/ruby/gems/3.4.0+0/gems/rake-12.3.3/lib/rake/rake_test_loader.rb:2: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
./home/yahonda/src/github.com/rails/sprockets/lib/rake/sprocketstask.rb:2: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
```

- Rake v13.2.0 does not depend on OpenStruct
https://github.com/ruby/rake/releases/tag/v13.2.0
ruby/rake#545

- Ruby 3.4.0dev emits OpenStruct warnings
https://bugs.ruby-lang.org/issues/20309
ruby/ruby#10428