Add complete AbstractGraph API and LEMON algorithm dispatch

[AJ0070]

Major Changes:

• LEMONGraph and LEMONDiGraph types implementing full AbstractGraph API
  (nv, ne, vertices, edges, has_vertex, has_edge, inneighbors, outneighbors, is_directed, edgetype)
• O(1) fast conversion reuse via cached node/edge arrays at construction
• GraphsInterfaceChecker.jl integration with formal API compliance validation
• LEMON algorithm dispatch via LEMONAlgorithm marker type:
  • maxweightedperfectmatching(g, weights, ::LEMONAlgorithm)
  • dijkstra_shortest_paths(g, src, distmx, ::LEMONAlgorithm)
• Extension support:
  • GraphsMatching.jl: minimum_weight_perfect_matching dispatch
  • GraphsOptim.jl: shortest_path dispatch
• Relevant tests are added
• Full documentation with usage examples

Fixes JuliaGraphs/Graphs.jl#447

AI Usage:
used GitHub copilot on auto mode.

Initially I generated skeleton with the AI. Implemented everything myself (used copilot whenever I felt complexity is high and I need to understand this more thoroughly). Then some key tests my self and asked copilot to give me complete test coverage so I don't miss out any edge cases (removed some unnecessary test it added). Then at last I asked him to update documentation according to the changes in the code (It added so many useless thing which I cleaned up).

[AJ0070]

this was a large diff so took me good amount of time and was also parallely working on networkx issue

[codecov]

Codecov Report

❌ Patch coverage is 94.98681% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.30%. Comparing base (bf9deb5) to head (4c60dee).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/LEMONGraphs.jl	92.27%	19 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #25       +/-   ##
===========================================
+ Coverage   80.95%   94.30%   +13.34%     
===========================================
  Files           1        3        +2     
  Lines          21      386      +365     
===========================================
+ Hits           17      364      +347     
- Misses          4       22       +18     

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[AJ0070]

failures are same as on main

[AJ0070]

@Krastanov Can I get review on this?

[AJ0070]

WIP: I will ping Krastanov once this is ready for review. this still requires good amount of work.

[AJ0070]

@Krastanov lmk when I can continue this.

[AJ0070]

@Krastanov gentle ping!

[AJ0070]

@Krastanov