Add native Pegasus and Zephyr plot helpers

[bernalde]

Closes #61

Summary

• Add DWave.draw_topology for Pegasus, Zephyr, WorkingGraph, sampler metadata, sample sets, and sampler objects.
• Add DWave.draw_embedding for returned embeddings over the full calibrated Pegasus/Zephyr working graph.
• Return a notebook-displayable Matplotlib figure by default, while supporting caller-supplied ax values.
• Document the plotting recipe and declare Matplotlib in the managed Python environment.

Tests

• DWAVE_API_TOKEN= JULIA_DEPOT_PATH=/home/bernalde/repos/DWave.jl/.julia-depot julia --project=. --startup-file=no test/topology.jl
• DWAVE_API_TOKEN= JULIA_DEPOT_PATH=/home/bernalde/repos/DWave.jl/.julia-depot julia --project=. --startup-file=no -e 'using Pkg; Pkg.test()'

The live DWave.Optimizer conformance tests were skipped because DWAVE_API_TOKEN was empty.

Branch Hygiene

• Base branch: main
• Source branch point: origin/main@a35fa52
• Head branch: feature/issue-61-topology-plots
• Stacked status: not stacked
• Prerequisite PRs: none

[bernalde]

No blocking findings from this review.

The implementation matches issue #61's core request: it adds native DWave.draw_topology and DWave.draw_embedding helpers, routes Pegasus and Zephyr working graphs through D-Wave NetworkX's canonical drawing functions, and keeps embedding overlays on the full calibrated working graph rather than only the used qubits. The metadata/sample-set overloads preserve the DWave.WorkingGraph(QUBOTools.metadata(sampleset)) path, and the README documents the notebook-facing usage.

Blocking issues: none.

Nonblocking issues: none.

Questions: none.

Tests run and outcomes:

• DWAVE_API_TOKEN= JULIA_DEPOT_PATH=/home/bernalde/repos/DWave.jl/.julia-depot julia --project=. --startup-file=no test/topology.jl passed locally against e1f6a662081ff803a14abf236fd1500a941663b1.
• GitHub CI is green for Julia 1.10 and Julia 1 on both Ubuntu and Windows.
• Live D-Wave sampler coverage was not exercised locally because DWAVE_API_TOKEN is empty; the existing live-token test path is skipped in that state.

Merge-readiness: the PR is ready for another maintainer's formal approval. This review is posted as COMMENT because the authenticated GitHub account (bernalde) is also the PR author, so GitHub will not accept a formal approval from this account.