Address PR review feedback: improve error handling, test clarity, and calculations

[Copilot]

Addresses all review comments from PR #73 on the parallelization changes.

Test improvements

• Renamed test_push_rules_correctness_with_lock → test_push_rules_parallel_with_lock to reflect parallel execution path
• Fixed comment mismatch (stated "5 batches" but tested 10)
• Added test_push_rules_partial_failure to verify error handling with partial batch failures
• Removed unused import

Error handling

Wrapped future.result() in try-except to handle unexpected exceptions beyond HTTPError:

for future in concurrent.futures.as_completed(futures):
    batch_idx = futures[future]
    try:
        result = future.result()
    except Exception as e:
        log.error("Unexpected error while processing batch %d: %s", batch_idx, e)
        log.debug("Unexpected exception details", exc_info=True)
        continue

Performance

Simplified batch count calculation from len(range(0, len(filtered_hostnames), BATCH_SIZE)) to (len(filtered_hostnames) + BATCH_SIZE - 1) // BATCH_SIZE

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