stream: do not pass readable.compose() output via Readable.from()

[Renegade334]

readable.compose() was intended to return the Duplex constructed by stream.compose(), and is documented as such.

However, because it was added as a "stream-returning operator", its output is being passed via Readable.from(), which constructs a new object-mode Readable by consuming the async iterator of the composed Duplex. This is inefficient in the best case, but causes breakage in a load of others:

• if the destination stream is writable-only, then the composed stream would be a non-readable Duplex, but would be returned as a readable Readable.
• if the source stream is a readable/writable Duplex, then the composed stream would be returned as a non-writable Readable, which misses the point of stream composition – the composed stream should be able to write to the head of the pipeline if it's writable, and read from the end if it's readable.
• the returned stream is always in object mode, clobbering the object mode detection of stream.compose().

This change gets rid of the "operator" semantics for readable.compose(), and makes it a standalone method which returns the unaltered composed Duplex stream from stream.compose().

Fixes: #55203

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[Renegade334]

There's no behaviour change here. Technically iterables are valid as "transformers" in stream.compose(), but since they ignore the source stream output entirely, it seems pointless to be documenting them here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.54%. Comparing base (768f3ba) to head (47933e0).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60907      +/-   ##
==========================================
- Coverage   88.56%   88.54%   -0.02%     
==========================================
  Files         703      703              
  Lines      208291   208287       -4     
  Branches    40169    40165       -4     
==========================================
- Hits       184472   184430      -42     
- Misses      15831    15869      +38     
  Partials     7988     7988              

Files with missing lines	Coverage Δ
lib/internal/streams/operators.js	96.14% <ø> (-0.30%)	⬇️
lib/internal/streams/readable.js	96.26% <100.00%> (+0.05%)	⬆️

... and 45 files with indirect coverage changes

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