Replace concat-stream w/ node:stream/consumers - #93

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

Closes GH-92.

stdin.js now reads streamIn with text() from node:stream/consumers instead of piping it into concat-stream.
concat-stream and @types/concat-stream leave dependencies, so CLI users no longer install them.
The stdin.js diff is easier to read with whitespace hidden: the callback body moved one indent level.

next is the second argument to .then(), as in lib/finder.js, not a .catch().
trough runs next once, so a .catch(next) would silently drop a throw that happens after next().
With .then(), that throw stays visible as an unhandled rejection.

Behavior changes:

• An error on streamIn now rejects the engine with that error.
  Before, .pipe() did not forward it and the process crashed with an uncaught exception.
  The new test in test/input.js covers this and fails on main.
• text() decodes with TextDecoder, which drops a leading UTF-8 byte order mark (BOM) on stdin.
  Files read from disk keep theirs.
  micromark and parse5 strip a BOM when parsing, so remark and rehype output stays the same.
• An object-mode streamIn now rejects with a TypeError.
  concat-stream turned such chunks into [object Object].
• A classic stream without Symbol.asyncIterator, such as a bare new Stream(), now rejects with TypeError: stream is not async iterable.
  streamIn accepts a NodeJS.ReadableStream, and that interface already requires Symbol.asyncIterator.
  Callers can wrap such a stream with new Readable().wrap(stream).
• The module needs Node.js 16.7 or later to load, which is when node:stream/consumers landed.
  CI runs Node.js 18 and latest.