Pre-load OMC shared libraries by absolute path in topological order

[SVAGEN26]

Problem

Tests in JKRT/OM.jl PR #44 (and any other downstream consumer of OMRuntimeExternalC.jl on Linux CI) fail with:

could not load library ".../libModelicaStandardTables.so"
libModelicaIO.so: cannot open shared object file: No such file or directory

even though libModelicaIO.so exists next to libModelicaStandardTables.so in lib/ext/shared/x86_64-linux-gnu/. Knock-on effect is 8 errored tests under OMRuntimeExternalC API and 10+ errored / failed tests under externalBuiltinTests.jl and downstream IMTK simulate paths in JKRT/OM.jl CI.

Root cause

Every .so in the libs-v0.1.0 release zip has its DT_RUNPATH baked to the original build host:

$ readelf -d libModelicaStandardTables.so | grep RUNPATH
RUNPATH  /home/johti17/Projects/OpenModelica/build_cmake/OMCompiler/SimulationRuntime/ModelicaExternalC:...

That path does not exist on consumer machines, so ld.so cannot resolve inter-library DT_NEEDED references on its own. The previous __init__ only pre-loaded libModelicaCallbacks, libModelicaIO and libModelicaExternalC, leaving libOpenModelicaRuntimeC, libomcgc, libModelicaMatIO, libModelicaStandardTables and libSimulationRuntimeC unresolved.

The ENV["LD_LIBRARY_PATH"] mutation in the old __init__ is ineffective on Linux because glibc's ld.so caches LD_LIBRARY_PATH at process start.

Fix

Pre-load every shipped library by absolute path with RTLD_GLOBAL in a fixed topological order:

libModelicaCallbacks
libomcgc
libOpenModelicaRuntimeC
libModelicaMatIO
libModelicaIO
libModelicaStandardTables
libModelicaExternalC
libSimulationRuntimeC

ld.so reuses the already-loaded library when it sees the same SONAME on a dependent load, so DT_NEEDED references are satisfied without relying on RUNPATH or LD_LIBRARY_PATH. SONAMEs in the release zip match the DT_NEEDED entries verbatim, so reuse is guaranteed.

libModelicaCallbacks is still loaded first so its symbols win global resolution and override the default OMC setjmp/longjmp-based error handlers.

Test evidence

Reproduced with the libs-v0.1.0 release zip on Linux x86_64, Julia 1.12.6:

Before (upstream master):

Attempting dlopen of: .../libModelicaStandardTables.so
FAILED: could not load library ".../libModelicaStandardTables.so"
libModelicaIO.so: cannot open shared object file: No such file or directory

After this PR:

Attempting dlopen of: .../libModelicaStandardTables.so
OK, handle = Ptr{Nothing}(0x0000000025f84850)

Identical error string in the before-state to what JKRT/OM.jl PR #44 CI emits.

Follow-ups not in this PR

• The release-side fix (rebuild the prebuilt libs with -Wl,-rpath,'$ORIGIN' -Wl,--enable-new-dtags) is still worth doing eventually so the package does not have to babysit ld.so. This PR makes the Julia-side correct regardless.
• The libs-v0.1.0 release ships libomcgc.so but pathSetup.jl does not track it; the new __init__ locates it by name from libdir, which keeps the change minimal. Tracking it in pathSetup.jl can come later if anything else needs to reference the path.
• The 404 for x86_64-linux-gnu-callbacks.tar.gz in build.jl is a separate, pre-existing release-artifact gap (local fallback handles it but should be cleaned up).

Refs JKRT/OM.jl#44