fix(promise): forward pool error events

[GiHoon1123]

Refs #3749

Promise pools inherit lifecycle events from the underlying core pool, but the error event was not forwarded and was not exposed in the promise pool types.

This adds error to the forwarded pool events and adds a matching pool.on('error', ...) overload for the promise API. The existing promise wrapper event test now covers error forwarding, and the TypeScript build tests cover the promise pool event signature.

Tests:

• npm run typecheck
• npm run lint
• npm run test:build

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.51%. Comparing base (f3a60bc) to head (90f419a).
⚠️ Report is 15 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4487   +/-   ##
=======================================
  Coverage   92.50%   92.51%           
=======================================
  Files          93       93           
  Lines       15909    15915    +6     
  Branches     2275     2275           
=======================================
+ Hits        14717    14723    +6     
  Misses       1192     1192           

Flag	Coverage Δ
compression-0	92.12% <100.00%> (+<0.01%)	⬆️
compression-1	92.49% <100.00%> (+<0.01%)	⬆️
static-parser-0	91.32% <100.00%> (+<0.01%)	⬆️
static-parser-1	91.44% <100.00%> (+<0.01%)	⬆️
tls-0	92.07% <100.00%> (+<0.01%)	⬆️
tls-1	92.51% <100.00%> (+<0.01%)	⬆️

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[sidorares]

@wellwelwel don't merge just yet. Wanted to check first that pool tracks idle connection errors at all - that might be not the case

[GiHoon1123]

Traced it — you're right to hold off.

PoolConnection's constructor swallows connection errors itself:

this.once('error', () => {
  this._removeFromPool();
});

_removeFromPool() → pool._removeConnection(this), which only takes the connection, not the error. So an idle connection's error never reaches Pool — there's nothing for Pool to emit, and nothing for this PR's forwarding to forward.

Making Pool actually emit those errors would need PoolConnection to forward them upward, guarded by a listenerCount check — without that guard, any app that's never called pool.on('error', ...) would crash on the next idle connection error instead of it being silently dropped like today. That's a real behavior change across both the callback and promise APIs, not something I want to fold into this PR.

Scoping this PR back to what #3749 actually asked for: the type is missing for an event inheritEvents already lists, so I'll keep it to that and drop the error addition to inheritEvents/promise.d.ts unless you'd rather track the idle-connection-error gap separately.

[GiHoon1123]

Correction on my last comment: inheritEvents didn't already list error before this PR — I added it (along with the promise.d.ts entry). Doesn't change the conclusion, just wanted the history accurate. Will drop both since Pool never actually emits error today.

[GiHoon1123]

Closing this. Once the error-forwarding piece is dropped there's nothing left to add here - the original request was for a type on an event Pool doesn't actually emit. If the idle-connection-error gap is worth fixing, that's a separate, bigger change to PoolConnection's own error handling, not this PR.