Issue #, if available:

Fixes #1360

Description of changes:

When a request is aborted, all three HTTP handlers (NodeHttpHandler, NodeHttp2Handler, FetchHttpHandler) reject with a generic new Error("Request aborted"). This makes it impossible for callers to determine which AbortSignal caused the abort, especially when using AbortSignal.any().

The fix adds a buildAbortError helper to each handler that uses AbortSignal.reason when available:

• If reason is an Error, it is used directly (preserving the caller's error type and stack).
• If reason is a non-Error value (e.g. a string), it is wrapped in an Error with name: "AbortError".
• If no reason is set (older runtimes or bare { aborted: true } signals), the existing "Request aborted" behavior is preserved.

// Before — always a generic error
const abortError = new Error("Request aborted");
abortError.name = "AbortError";
reject(abortError);

// After — uses the signal's reason when available
const abortError = buildAbortError(abortSignal);
reject(abortError);

All six abort sites across the three handlers were updated (two per handler: the early-abort check and the onAbort listener).

Tests added to node-http-handler.spec.ts:

• Rejects with the custom Error reason directly
• Falls back to default "Request aborted" when no reason is set
• Wraps non-Error string reasons in an Error with name: "AbortError"

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