Add lazy option to QuantumOpticsRepr - #81

Summary

• add a lazy::Bool=false field to QuantumOpticsRepr
• preserve the existing QuantumOpticsRepr(cutoff) positional constructor
• document that lazy output is opt-in for downstream packages

This supports qojulia/QuantumOptics.jl#521, where QuantumSymbolics needs to request structure-preserving QuantumOptics lazy operators.

Testing

• Not run locally: Julia is not installed in this environment.

AI assistance disclosure

AI assistance was used to inspect the codebase and draft this patch.