[iree-benchmark-module] Unify sync, async and dispatch execution (#24986)

`iree-benchmark-module` had separate synchronous, asynchronous, and
generated-dispatch execution paths that applied output processing,
replay capture, and profiling flushes inconsistently. Run them through
one batch lifecycle so discovery resolves each function's ABI and
iteration accounting once and every execution model shares the measured
loop.

The shared lifecycle fixes several inconsistencies:

- Retain asynchronous outputs for `--enable_output_processing`.
- Supply fence arguments for discovered asynchronous functions.
- Use the generated repeat count for dispatch benchmarks selected with
`--function`.
- Handle non-power-of-two `--batch_concurrency` without reading past the
invocation list.
- Return recording devices from context setup so asynchronous fences
participate in replay capture.

Errors go to stderr with `EXIT_FAILURE`, matching `iree-run-module`.
Output processing requires a single benchmarked function, and
nonpositive batch size or concurrency is rejected. Device profiling ends
before output processing.

Assisted by AI.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>