events: report original once() listener on removal

[vedchaudhari]

If a once() listener is removed while other listeners are still on the same event, the 'removeListener' event gets Node's internal once() wrapper instead of the original listener:

const EventEmitter = require('node:events');
function f() {}
function g() {}
const ee = new EventEmitter();
ee.once('x', f);
ee.on('x', g);
ee.on('removeListener', (type, listener) => console.log(listener === f));
ee.emit('x');
// before: false (listener is the internal wrapper)
// after:  true

This was fixed in #6394 (2016) and documented, but #33596 (2020) removed the unwrapping from the multi-listener path. The existing test only used a single listener, so CI didn't catch it.

This unwraps the listener the same way the single-listener path already does, and adds a test with a second listener. The stream, domain and event tests pass.

Benchmark: events/ee-add-remove.js (30 runs)

                                                                  confidence   improvement   accuracy (*)    (**)   (***)
events/ee-add-remove.js n=1000000 removeListener=0 newListener=0   **             -0.98 %   ±0.59%  ±0.78%  ±1.02%
events/ee-add-remove.js n=1000000 removeListener=1 newListener=0    *             +1.58 %   ±1.39%  ±1.86%  ±2.44%
events/ee-add-remove.js n=1000000 removeListener=0 newListener=1    *             -1.67 %   ±1.45%  ±1.94%  ±2.52%
events/ee-add-remove.js n=1000000 removeListener=1 newListener=1                  +0.08 %   ±1.42%  ±1.89%  ±2.46%

The changed line only runs when a 'removeListener' listener is attached, so the removeListener=0 rows run the same code as before and their ±1–2% is noise.

I used Claude Code to find the bug and write the fix and test. I reproduced it, reviewed the change, and ran the tests and benchmark myself.

Refs: #5551
Refs: #6394
Refs: #33596

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.42%. Comparing base (dd9777b) to head (7985f64).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66621      +/-   ##
==========================================
- Coverage   92.78%   90.42%   -2.36%     
==========================================
  Files         422      791     +369     
  Lines      193692   276585   +82893     
  Branches    29881    53114   +23233     
==========================================
+ Hits       179714   250110   +70396     
- Misses      13650    16872    +3222     
- Partials      328     9603    +9275     

Files with missing lines	Coverage Δ
lib/events.js	99.60% <100.00%> (+6.28%)	⬆️

... and 498 files with indirect coverage changes

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