Add JuliaC trim compile workload

[quinnj]

Summary

• add a JuliaC trim-compile test workload that runs from the normal JSON.jl test suite on supported Julia versions
• resolve JuliaC in a small temporary trim project so JSON.jl's Julia 1.9 test target remains compatible
• exercise trim-safe public entrypoints for lazy reads, lazyfile, JSON.Object, JSON.JSONText, JSON.Null, JSON.lower, JSON.json, and JSON.print

Notes

Materializing JSON.parse, parsefile, parse!, and isvalidjson currently expands parser / StructUtils paths that produce trim verifier errors, so this PR establishes the always-on green harness first without changing performance-sensitive parser code.

Validation

• julia --startup-file=no --history-file=no -e 'using Pkg; root = pwd(); mktempdir() do tmp; Pkg.activate(tmp); Pkg.develop(PackageSpec(path = root)); Pkg.test("JSON"); end'
• julia +1.9 --startup-file=no --history-file=no --project= -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.test("JSON")'
• julia +1.13.0-rc1 --startup-file=no --history-file=no -e 'using Pkg; root = pwd(); tmp = mktempdir(); Pkg.activate(tmp); Pkg.develop(PackageSpec(path = root)); Pkg.instantiate(); @eval using JSON; include(joinpath(root, "test", "trim_compile_tests.jl"))'

Co-authored by Codex

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.41%. Comparing base (e5ef310) to head (fb92cb2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #471   +/-   ##
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  Coverage   90.41%   90.41%           
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  Files           7        7           
  Lines        1419     1419           
=======================================
  Hits         1283     1283           
  Misses        136      136           

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