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 72.97297% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.43%. Comparing base (8da9a5e) to head (9dfc4b8).

Files with missing lines	Patch %	Lines
src/LEMONGraphs.jl	77.22%	23 Missing ⚠️
ext/LEMONGraphsGraphsMatchingExt.jl	23.80%	16 Missing ⚠️
ext/LEMONGraphsGraphsOptimExt.jl	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   80.00%   72.43%   -7.57%     
==========================================
  Files           1        3       +2     
  Lines          20      156     +136     
==========================================
+ Hits           16      113      +97     
- Misses          4       43      +39     

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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.