Indexing out of bounds on directed graphs.

I'm not entirely sure whether this is supposed to work with directed graphs, if not it would be nice with a clear error stating that.

Assuming that it should work, there are some bugs to track down:
```
$ julia --check-bounds=yes
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.12.4 (2026-01-06)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org release
|__/ |

julia> using GraphsTreewidth, Graphs

julia> g = erdos_renyi(5, 0.5, is_directed = true, seed = 1)
{5, 9} directed simple Int64 graph

julia> Solver(g)
ERROR: BoundsErrorLight: attempt to access array of type FixedSizeArrays.FixedSizeArray{Int64, 1, Memory{Int64}} and shape (10029,) at index [-1]
Stacktrace:
[1] throw_boundserrorlight
@ ~/.julia/packages/FixedSizeArrays/VHLXx/src/BoundsErrorLight.jl:32 [inlined]
[2] check_bounds_light
@ ~/.julia/packages/FixedSizeArrays/VHLXx/src/BoundsErrorLight.jl:37 [inlined]
[3] getindex
@ ~/.julia/packages/FixedSizeArrays/VHLXx/src/FixedSizeArray.jl:166 [inlined]
[4] hamf_impl!(norig::Int64, n::Int64, nbelts::Int64, nbbuck::Int64, iwlen::Int64, pe::FixedSizeArrays.FixedSizeArray{…}, pfree::Int64, len::FixedSizeArrays.FixedSizeArray{…}, iw::FixedSizeArrays.FixedSizeArray{…}, nv::FixedSizeArrays.FixedSizeArray{…}, elen::FixedSizeArrays.FixedSizeArray{…}, last::FixedSizeArrays.FixedSizeArray{…}, degree::FixedSizeArrays.FixedSizeArray{…}, wf::FixedSizeArrays.FixedSizeArray{…}, next::FixedSizeArrays.FixedSizeArray{…}, w::FixedSizeArrays.FixedSizeArray{…}, head::FixedSizeArrays.FixedSizeArray{…})
@ CliqueTrees.AMFLib ~/.julia/packages/CliqueTrees/Tzv8B/src/AMFLib.jl/src/AMFLib.jl:1254
[5] amf_impl!(norig::Int64, n::Int64, nbbuck::Int64, iwlen::Int64, pe::FixedSizeArrays.FixedSizeArray{…}, len::FixedSizeArrays.FixedSizeArray{…}, iw::FixedSizeArrays.FixedSizeArray{…}, nv::FixedSizeArrays.FixedSizeArray{…}, elen::FixedSizeArrays.FixedSizeArray{…}, last::FixedSizeArrays.FixedSizeArray{…}, degree::FixedSizeArrays.FixedSizeArray{…}, wf::FixedSizeArrays.FixedSizeArray{…}, next::FixedSizeArrays.FixedSizeArray{…}, w::FixedSizeArrays.FixedSizeArray{…}, head::FixedSizeArrays.FixedSizeArray{…}, vwght::FillArrays.Ones{…}, xadj::FixedSizeArrays.FixedSizeArray{…}, adjncy::FixedSizeArrays.FixedSizeArray{…})
@ CliqueTrees.AMFLib ~/.julia/packages/CliqueTrees/Tzv8B/src/AMFLib.jl/src/AMFLib.jl:131
[6] amf(n::Int64, vwght::FillArrays.Ones{…}, xadj::FixedSizeArrays.FixedSizeArray{…}, adjncy::FixedSizeArrays.FixedSizeArray{…})
@ CliqueTrees.AMFLib ~/.julia/packages/CliqueTrees/Tzv8B/src/AMFLib.jl/src/AMFLib.jl:86
[7] amf
@ ~/.julia/packages/CliqueTrees/Tzv8B/src/elimination_algorithms.jl:2092 [inlined]
[8] permutation
@ ~/.julia/packages/CliqueTrees/Tzv8B/src/elimination_algorithms.jl:1376 [inlined]
[9] cliquetree(weights::FillArrays.Ones{…}, graph::SimpleDiGraph{…}, alg::CliqueTrees.AMF, snd::CliqueTrees.Maximal)
@ CliqueTrees ~/.julia/packages/CliqueTrees/Tzv8B/src/clique_trees.jl:127
[10] cliquetree
@ ~/.julia/packages/CliqueTrees/Tzv8B/src/clique_trees.jl:99 [inlined]
[11] #cliquetree#51
@ ~/.julia/packages/CliqueTrees/Tzv8B/src/clique_trees.jl:81 [inlined]
[12] cliquetree
@ ~/.julia/packages/CliqueTrees/Tzv8B/src/clique_trees.jl:76 [inlined]
[13] #Solver#7
@ ~/.julia/dev/GraphsTreewidth/src/solvers.jl:8 [inlined]
[14] Solver(graph::SimpleDiGraph{Int64})
@ GraphsTreewidth ~/.julia/dev/GraphsTreewidth/src/solvers.jl:7
```