Hamiltonian loading and data storage

[detrin]

Serialize and deserialize aggregates, Hamiltonians, and simulation results to disk for reproducibility and data sharing.

What needs to be implemented

1. Save/load Aggregate — serialize the full Aggregate (core, tools, operators) to JLD2 format
2. Save/load SimulationResult — store time series and metadata
3. Import from external formats — read Hamiltonians from CSV/JSON for interop with other packages
4. API — save_aggregate(filename, agg), load_aggregate(filename), save_result(filename, result), load_result(filename)

New dependency

JLD2.jl (consider as package extension)

Proposed files

• src/io.jl or ext/IOExt.jl — serialization functions
• test/test_io.jl — round-trip tests