Add configurable Dask frame execution with SLURM-backed HPC support

[harryswift01]

Summary

This PR adds configurable parallel frame-by-frame execution to CodeEntropy using Dask, with support for both local Dask workers and SLURM-backed HPC execution. It also adds runtime submission support for SLURM master jobs, validates the new parallel/HPC configuration options, and updates the documentation to explain the new arguments and parallel execution modes.

Changes

Parallel frame execution:

• Added Dask-based frame-level execution in LevelDAG.
• Added a parent-side reduction model where Dask workers compute frame-local covariance outputs and the main process reduces them into shared accumulators.
• Avoided broadcasting mutable trajectory/shared state to workers to prevent frame interference.
• Excluded parent-only objects and covariance accumulator aliases from worker payloads.
• Added sequential fallback behaviour when parallel execution is disabled, no Dask client is available, or only one frame is selected.

Local Dask and SLURM/HPC configuration:

• Added new configuration arguments for local Dask execution, including parallel_frames, use_dask, dask_workers, and dask_threads_per_worker.
• Added SLURM/HPC configuration options, including hpc, submit, hpc_queue, hpc_nodes, hpc_cores, hpc_processes, hpc_memory, hpc_walltime, hpc_account, hpc_qos, hpc_constraint, conda_path, conda_exec, and conda_env.
• Added HPCDaskManager for configuring SLURM-backed Dask clusters and generating/submitting master SLURM scripts.
• Added runtime handling for submit=True, allowing CodeEntropy to submit a master SLURM job and exit before starting local analysis.
• Added validation for local Dask, HPC, submit, and conda-related options.

Tests and documentation:

• Added unit tests for parallel frame execution, worker payload filtering, Dask submission, failure handling, and completed-frame validation.
• Added tests for local Dask and HPC workflow configuration paths.
• Added tests for SLURM helper behaviour, submit script generation, and submit error handling.
• Merged overlapping LevelDAG tests into a single test file to reduce duplication.
• Updated the getting started documentation with the new configuration arguments.
• Added a new documentation section explaining local Dask execution, SLURM/HPC Dask execution, and submit mode.

Impact

• Enables CodeEntropy to process frame-local covariance calculations in parallel.
• Provides a scalable path for larger trajectories using local Dask or SLURM-backed Dask workers.
• Keeps covariance reduction deterministic by performing reductions in the parent process.
• Improves HPC usability by allowing users to generate and submit SLURM master jobs directly from CodeEntropy.
• Adds validation to catch invalid parallel/HPC configuration before execution.
• Expands test coverage for the new parallel, HPC, and submit code paths.
• Updates user-facing documentation so users can configure and run sequential, local parallel, HPC, or submit-mode workflows.