Tests: add GraphsInterfaceChecker harness (placeholder)

[Ashutosh0x]

• Add GraphsInterfaceChecker and BenchmarkTools to test deps\n- Add placeholder compliance test to ratchet toward API coverage\n- Keep current algorithms unchanged; this is scaffolding only

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 12.00%. Comparing base (5841fbe) to head (e011123).

Files with missing lines	Patch %	Lines
src/LEMONGraphs.jl	25.00%	6 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (5841fbe) and HEAD (e011123). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (5841fbe)	HEAD (e011123)
	5	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #6       +/-   ##
===========================================
- Coverage   81.81%   12.00%   -69.82%     
===========================================
  Files           1        1               
  Lines          22       25        +3     
===========================================
- Hits           18        3       -15     
- Misses          4       22       +18     

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[Krastanov]

Thanks for looking into this! There seems to be a lot of unrelated changes. Please remove them so that the PR is on a single topic.