Define equality for `TruncationStrategy`s

[Yue-Zhengyuan]

In PEPSKit, when a trunc::SiteDependentTruncation is passed to the time evolution algorithm of a bipartite state, we need to check if trunc matches the bipartite structure by something like:

function _is_bipartite(trunc::SiteDependentTruncation)
    (size(trunc, 2) == size(trunc, 3) == 2) || (return false)
    # d = 1, 2 for x, y bond truncations
    for (d, c) in Iterators.product(1:2, 1:2)
        (trunc[d, 1, c] == trunc[d, 2, _next(c, 2)]) || (return false)
    end
    return true
end

This requires the equality of TruncationStrategys to be well-defined. Currently TruncationSpace (only exists in TensorKit) doesn't work for all sectors:

using TensorKit
t1 = truncspace(ℂ^3)
t2 = truncspace(ℂ^3)
@show t1 == t2 # true
t1 = truncspace(Z3Space(0 => 2, 2 => 1))
t2 = truncspace(Z3Space(0 => 2, 2 => 1))
@show t1 == t2 # true
t1 = truncspace(U1Space(0 => 1, 1 => 2))
t2 = truncspace(U1Space(0 => 1, 1 => 2))
@show t1 == t2 # false
t1 = truncspace(SU2Space(0 => 1, 1 => 2))
t2 = truncspace(SU2Space(0 => 1, 1 => 2))
@show t1 == t2 # false

I haven't tested the ones introduced by MatrixAlgebraKit.

[sanderdemeyer]

Okay, maybe as a fix we can define the equality for TruncationStrategy as something like

all([getfield(t1, f) == getfield(t2, f) for f in fieldnames(typeof(t1))])

this returns true for all examples you have given.

[Yue-Zhengyuan]

I think this is general enough to be directly put in MatrixAlgebraKit and work for all TruncationStrategys (even for NoTruncation with no fields, since all([]) = true.