Fix Downgrade (QA): remove PATH solve from precompile workload (intermittent libpath50 segfault)

[ChrisRackauckas-Claude]

Problem

The Downgrade (QA) job on main is red. It fails during a from-scratch precompilation of the package with a segfault in PATHSolver's native library (libpath50):

[3632] signal (11.1): Segmentation fault
in expression starting at .../src/precompilation.jl:3
Output_Printf at .../datadeps/libpath50/libpath50.so (unknown line)
ERROR: Failed to precompile ComplementaritySolve ...

Because precompilation aborts, the QA testsets (Aqua, ExplicitImports) error before they run.

The previous Downgrade fix (#64) resolved the earlier Unsatisfiable requirements resolution failures in all three groups; Core and Applications are now green. QA was the last remaining red, and its failure is a different cause: this precompile segfault.

Root cause

The @compile_workload ends by actually solving an MCP with PATHSolverAlgorithm(), which calls into the PATH native C library (libpath50.so) from inside the precompile worker process. That native call segfaults intermittently. Reproduced locally on Julia 1.10.11 with the downgrade-resolved versions (PATHSolver 1.4.0, ForwardDiff 1.0.1, Zygote 0.7.5): roughly 1 in ~20 cold-cache precompiles crashes with the identical signature (signal (11): Segmentation fault in precompilation.jl, Output_Printf at libpath50.so). Every Downgrade run does a cold precompile, so it hits this regularly.

It is not a Julia-code bug and not a resolution problem — it is the PATH native library being unsafe to invoke inside the precompile worker. (test/aqua.jl already disables persistent_tasks with the note "PATHSolver precompile workload triggers persistent task detection", and InteriorPointMethod is already excluded from the workload for stability.)

Fix

Remove the PATH solve from the precompile workload. Invoking the PATH solver is the only operation that loads/calls libpath50 during precompilation, and native C-library calls are not what precompilation caches in the first place — so excluding it loses no meaningful cached coverage while making precompilation deterministic.

Local verification (Julia 1.10.11, downgrade-resolved versions)

• Before the fix: cold-cache QA precompile segfaults intermittently (reproduced the exact CI signature).
• After the fix: 8/8 cold-cache QA runs pass (Aqua: 3 pass / 1 broken-as-declared; ExplicitImports: 2 pass), zero segfaults.
• Package still precompiles cleanly at latest versions on Julia 1.10.

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Please ignore until reviewed by @ChrisRackauckas

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Companion CI fix: The CUDA Core / CUDA Applications reds seen on main and on this branch are a separate, infrastructure-level failure — the two GPU matrix jobs race on the shared self-hosted ~/.gitconfig inside codecov-action's safe.directory setup (tests pass; the post-step exits 255). That is fixed in #67, not here. This PR remains focused on the Downgrade (QA) precompile segfault.