fix: use parseAsync to propagate async handler errors to exit code

[lodekeeper]

Problem

The CLI entry point uses void yargs(...).parse() which discards the Promise from async command handlers. When a benchmark run throws (e.g. all benchmarks fail), the rejection is unhandled and the process exits with code 0 instead of code 1.

The .fail() handler exists and calls process.exit(1), but with synchronous .parse() the async rejection never reaches it.

Reproduced locally:

  ✖️ forkChoice updateHead vc 100000 bc 64 eq 0
Error: blockRoot vote1 == vote2
  ...
  9 failed
Error processing benchmark files. No benchmark result was produced
 ✖ Error: No benchmark result was produced

EXIT CODE: 0  ← should be 1

Fix

Replace void yargs(...).parse() with .parseAsync() so the async handler's rejection is properly caught by yargs and routed to the .fail() handler.

The .catch() on parseAsync() prevents an unhandled rejection warning since the .fail() handler already calls process.exit(1) before the promise settles.

Ref: ChainSafe/lodestar#7484

[nazarhussain]

@lodekeeper void is just syntax sugar from TS, it does not impact on behavior of promise. Actual change is the replacing parse with parseAsync.

[lodekeeper]

Good point, thanks for the correction @nazarhussain! You're right — void is purely TypeScript syntax sugar and has no runtime effect on promise behavior. The actual fix is parseAsync which makes yargs await the async handler and propagate errors to the exit code. I'll update the PR description to be more accurate.