Make get_effects and get_exct shared generics

[jishnub]

src/CthulhuCompiler.jl imports the CallInfo accessors from Cthulhu so that both compiler integrations extend the same generic functions — but get_effects and get_exct are missing from that import list, and get_effects is instead defined fresh at the bottom of the file.

Since CthulhuCompiler.jl is included once into Cthulhu and again into CthulhuCompilerExt when Compiler.AbstractInterpreter !== Base.Compiler.AbstractInterpreter, this means Cthulhu.get_effects and CthulhuCompilerExt.get_effects become two distinct functions in that configuration, and Cthulhu.get_effects(info) raises a MethodError for any CallInfo produced by the extension. get_ci, get_rt and the rest are unaffected because they are imported.

This adds function get_effects end / function get_exct end next to the existing stubs in callsite.jl (they had no owning declaration before) and adds both names to the import list.

No behaviour change in the common case, where Compiler reexports Base.Compiler and the extension is a no-op.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (2c33b9a) to head (28f0c59).
⚠️ Report is 99 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #707    +/-   ##
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  Coverage    0.00%   0.00%            
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  Files           9      22    +13     
  Lines        1556    1808   +252     
=======================================
- Misses       1556    1808   +252     

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[serenity4]

Makes sense, thanks!