feat(openquant): add AFML Ch20 hpc_parallel utilities module

[Sean-Koval]

Summary

• add new hpc_parallel module implementing AFML Chapter 20 atom->molecule parallel execution primitives
• provide serial and threaded execution modes with mp_batches oversubscription controls
• implement linear and nested partition strategies with progress + throughput diagnostics
• add async dispatch handle for background execution and typed error propagation
• add module docs and AFML docs-state entries for Chapter 20 coverage

Testing

• cargo test -p openquant --test hpc_parallel
• cargo bench -p openquant --bench hpc_parallel_scaling --no-run
• cargo test -p openquant --lib --tests
• PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 cargo clippy --all-targets --all-features -- -D clippy::correctness -D clippy::suspicious
• cargo bench -p openquant --bench hpc_parallel_scaling -- --sample-size 10