Add VNAlgorithm dispatch for very_nauty C library algorithms

[nenadilic84]

Summary

Adds a VNAlgorithm dispatch type that routes graph algorithms to the very_nauty C library implementation, following the pattern specified in JuliaGraphs/Graphs.jl#448.

New API

using VNGraphs
import Graphs

g = Graphs.cycle_graph(5)

# Dispatch to very_nauty via VNAlgorithm()
Graphs.is_connected(g, VNAlgorithm())        # true
Graphs.connected_components(g, VNAlgorithm()) # [[1, 2, 3, 4, 5]]

# very_nauty-specific algorithms (not in Graphs.jl)
chromatic_number(g, VNAlgorithm())       # 3  (exact, via exhaustive search)
edge_chromatic_number(g, VNAlgorithm())  # 3
clique_number(g, VNAlgorithm())          # 2

Design

• VNAlgorithm is an exported dispatch type
• All methods accept any AbstractGraph and auto-convert to VNGraph internally when needed
• is_connected and connected_components extend existing Graphs.jl functions
• chromatic_number, edge_chromatic_number, and clique_number are new functions exported from VNGraphs (these algorithms don't exist in Graphs.jl yet)

Algorithms dispatched

Function	C library call	Notes
Graphs.is_connected(g, ::VNAlgorithm)	graph_connected	Returns Bool
Graphs.connected_components(g, ::VNAlgorithm)	graph_nclusters + cluster labels	Returns Vector{Vector{Int}}
chromatic_number(g, ::VNAlgorithm; timeout=0)	graph_chromatic_number	Exact, optional timeout
edge_chromatic_number(g, ::VNAlgorithm; timeout=0)	graph_edge_chromatic_number	Exact, optional timeout
clique_number(g, ::VNAlgorithm)	graph_clique_number	Exact

Bounty checklist progress (Graphs.jl#448)

• Dispatch from operations to very_nauty implementation via VNAlgorithm
• Declare missing algorithms in Graphs.jl (chromatic_number, clique_number — separate PR to Graphs.jl)

All 307 tests pass locally on Julia 1.11.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.52%. Comparing base (b1faf64) to head (8e2947f).
⚠️ Report is 12 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #19       +/-   ##
===========================================
+ Coverage   45.90%   86.52%   +40.62%     
===========================================
  Files           1        1               
  Lines          61      141       +80     
===========================================
+ Hits           28      122       +94     
+ Misses         33       19       -14     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[nenadilic84]

All CI test jobs pass across all platforms (ubuntu, windows, macOS x64, macOS aarch64).

The only failing check is Documentation — same pre-existing issue as PR #18 (no docs/make.jl in the repo).

[Krastanov]

There were a few other PRs by you on projects for which we have bounties. Some of them have received full or partial reviews over the last few month or two without a follow up from you. Of course, as a volunteer you do not owe us anything, and we are always grateful when someone contributes to our packages. However, given the lack of response, and the fact that the PRs seem to have been generated by an LLM, reviewing more of these PRs creates a very significant burden on the reviewers. Thus, I will proceed to close this PR.

It is certainly possible you just happen to be too busy to respond to those PR comments right now. If that is the case, please feel free to reopen PRs you would like to pursue whenever you find some free time -- humans jumping on board to help is always appreciated.