General interface for gauge constraints of tensor networks

A design could be:

abstract type AbstractGaugeConstraint end

struct ITensorNetwork{V,C<:AbstractGaugeConstraint} <: AbstractITensorNetwork{V}
  data_graph::DataGraph{V,ITensor,ITensor,NamedGraph{V},NamedEdge{V}}
  gauge_constraint::C
end

# No gauge constraint, this could be the default
# fallback.
struct NoGaugeConstraint <: AbstractGaugeConstraint
end

# Symmetric gauge, stores the message tensors
# Λₑ which are the same as the Vidal gauge bond
# matrices
struct SymmetricGauge{V} <: AbstractGaugeConstraint
  message_tensors::DataGraph{V,ITensor,ITensor,NamedGraph{V},NamedEdge{V}}
end

# Vidal gauge, stores the edges where the bond matrices
# Λₑ are present. The bond matrices themselves are
# stored in the `data_graph` of the ITensorNetwork.
struct VidalGauge{E} <: AbstractGaugeConstraint
  edges::Vector{E}
end

# isoTNS gauge, stores the vertices that
# defines the gauge center region.
struct IsometricGauge{v} <: AbstractGaugeConstraint
  center::Vector{V}
end

The issue contains a Julia design sketch but names no files, tests, or entry points. Start by examining the proposed ITensorNetwork and AbstractGaugeConstraint types, then determine how the listed gauge variants should fit the project. Completion criteria and required tests are not specified, so the interface needs agreement before implementation.