Fix --exec-batch command order when batching

[cyphercodes]

Summary

• Preserve --exec-batch command order when multiple batch commands are split into batches.
• Keep the existing streaming path for a single --exec-batch command.
• Add a regression test and changelog entry.

Fixes #2033

Tests

• cargo test test_exec_batch_multi_with_limit_preserves_command_order -- --nocapture
• cargo test test_exec_batch -- --nocapture
• cargo test
• cargo clippy --all-targets --all-features -- -Dwarnings
• cargo fmt --all -- --check
• git diff --check

AI disclosure

Implemented with assistance from an AI coding tool; changes were reviewed and verified locally.