Add support for CompositeReadIO#close.

[ioquatix]

Required to fix socketry/async-http-faraday#32.

Faraday's implementation of #close expects CompositeReadIO to implement close:

 0.84s     warn: Async::Task: Writing #<Async::HTTP::Faraday::BodyWrapper:0x0000000128e1ca48> to #<Async::HTTP::Protocol::HTTP2::Response::Stream:0x0000000128a60f08>. [oid=0x2bc] [ec=0x2d0] [pid=37892] [2024-02-07 22:55:46 +1300]
               | Task may have ended with unhandled exception.
               |   NoMethodError: undefined method `close' for an instance of Multipart::Post::CompositeReadIO
               |   → /Users/samuel/.gem/ruby/3.3.0/gems/faraday-multipart-1.0.4/lib/faraday/multipart/file_part.rb:112 in `each'
               |     /Users/samuel/.gem/ruby/3.3.0/gems/faraday-multipart-1.0.4/lib/faraday/multipart/file_part.rb:112 in `close'
               |     lib/async/http/faraday/adapter.rb:30 in `close'

Types of Changes

• Bug fix.
• New feature.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.