Add Q-matrix preprocessing permutation

[bernalde]

Summary

• Add deterministic Q-matrix preprocessing that uses a reverse Cuthill-McKee-style ordering to place coupled variables closer in the MPS tensor order.
• Preserve caller-facing variable order by unpermuting Solution samples and probability checks.
• Wire the existing preprocess optimizer attribute through the QUBODrivers/JuMP solve path.
• Add an exact one-variable solve path for reduced QUBOs where ITensor DMRG is not applicable.

Tests run

• julia +1.12 --project=. -e 'using Pkg; Pkg.test()' - passed.
• julia +1.12 --project=docs/ docs/make.jl - passed.
• julia +1.10 -e 'import Pkg; Pkg.activate(; temp=true); Pkg.develop(path=pwd()); Pkg.test("TenSolver"; coverage=true, julia_args=["--check-bounds=yes", "--compiled-modules=yes", "--depwarn=yes"], force_latest_compatible_version=false, allow_reresolve=true)' - passed.

Notes about tests not run

• julia --project=. -e 'using Pkg; Pkg.test()' was attempted first, but the default local Julia is 1.11.5 while the checked-out manifest was resolved with Julia 1.12.6, causing Pkg to fail before package code loaded with a missing OpenSSL_jll source error. The suite was rerun successfully with julia +1.12.
• julia +1.10 --project=. -e 'import Pkg; Pkg.test(; coverage=true, julia_args=["--check-bounds=yes", "--compiled-modules=yes", "--depwarn=yes"], force_latest_compatible_version=false, allow_reresolve=true)' hit the same local manifest mismatch. The Julia 1.10 test was rerun from a temporary environment that develops this checkout, matching CI's resolved QUBODrivers v0.3.4 path without mutating tracked manifests.

Closes #12

[bernalde]

No blocking issues found. I inspected the PR diff, surrounding solver/Solution/JuMP code, tests, docs, README, and CI workflows. The implementation keeps caller-facing bit order stable while using the permuted tensor order internally, and the one-variable fallback is consistent with the existing API surface.
Tests run locally:

• julia +1.12 --project=. -e 'using Pkg; Pkg.test()' passed.
• julia +1.12 --project=docs/ docs/make.jl passed.
• julia +1.12 --project=test -e 'push!(LOAD_PATH, pwd()); using Test, TenSolver, JuMP, LinearAlgebra; ...' targeted preprocessing/JuMP/one-variable smoke passed.