Use the concrete Base.RefValue instead of abstract Ref in structs

[JamesWrigley]

This helps type-stability and prevents invalidations. Specifically, it prevents these invalidations on Julia 1.12 with UnsafePointers.jl (CC @cjdoris):

 inserting getindex(p::UnsafePointers.UnsafePtr{T}) where T @ UnsafePointers ~/git/UnsafePointers.jl/src/UnsafePointers.jl:105 invalidated:
   mt_backedges: 1: signature Tuple{typeof(getindex), Ref{Bool}} triggered MethodInstance for JuliaInterpreter.add_breakpoint_if_match!(::JuliaInterpreter.FrameCode, ::JuliaInterpreter.BreakpointSignature) (1 children)
                 2: signature Tuple{typeof(getindex), Ref{Bool}} triggered MethodInstance for JuliaInterpreter.add_breakpoint_if_match!(::JuliaInterpreter.FrameCode, ::JuliaInterpreter.BreakpointFileLocation) (273 children)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.81%. Comparing base (376d172) to head (f3a16cd).
⚠️ Report is 80 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #702      +/-   ##
==========================================
+ Coverage   81.03%   84.81%   +3.78%     
==========================================
  Files          12       12              
  Lines        2636     2726      +90     
==========================================
+ Hits         2136     2312     +176     
+ Misses        500      414      -86     

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[aviatesk]

Thanks for your contribution!

[JamesWrigley]

Would it be possible to tag a new release with this?

[aviatesk]

Tagged a new release.

[JamesWrigley]

Thanks ❤️