fix(process): apply one timeout rule to both execFileOutput modes

Node's execFile timeout contract differs by supported runtime: Node 22
and 24 accept any non-negative integer (their timers clamp anything
above 2^31-1 to 1 ms), while Node 26 caps it at Number.MAX_SAFE_INTEGER.
Mirroring either left stoppable and plain commands disagreeing on one
runtime. Validate a safe non-negative integer before spawning in both
modes, so every supported runtime gives the same answer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/process/ExecFileOutput.test.ts

@@ -123,8 +123,8 @@ describe.skipIf(process.platform === "win32")(
       expect(await readFile(stopped, "utf8")).toBe("SIGINT");
     });
 
-    it.each([-1, Number.NaN, 1.5, Number.POSITIVE_INFINITY])(
-      "refuses a malformed timeout (%s) before starting the command, as execFile does",
+    it.each([-1, Number.NaN, 1.5, Number.POSITIVE_INFINITY, 2 ** 53])(
+      "refuses a malformed timeout (%s) in both modes before starting the command",
       async (timeout) => {
         // Starting this command would fail with ENOENT instead.
         await expect(