This aligns Readable.toWeb(stream) termination handling with
eos(stream, { writable: false }).

Changes:

• add regression tests for half-open duplex termination
• add regression coverage for adapter creation before and after
  end(), destroy(), and destroy(error)
• preserve terminated Readable adapter state, including closed/error
  state and byte stream type, regardless of when the adapter is created
• let Readable.toWeb() reuse eos() immediate completion handling
  for already-terminated streams
• add regression coverage for the synchronous internal EOS callback
  path, including listener cleanup and BYOB termination

Tests:

• make lint
• ./configure && make -j4 test