Fix ModelingToolkitBase QA imports on Julia 1.11

[ChrisRackauckas-Claude]

Failing before

On clean upstream/master at 24e9206e21263ae41c43148434bd4c2dd1bf1977, Julia 1.11.9 failed the ModelingToolkitBase QA group:

GROUP=ModelingToolkitBase_QA ~/.juliaup/bin/julia +1.11 --project=lib/ModelingToolkitBase -e 'using Pkg; Pkg.test()'

Test Summary: | Pass  Total     Time
JET Tests     |   54     54  3m39.9s

Test Summary:                                  | Pass  Error  Total     Time
Aqua Tests                                     |   19      2     21  5m06.8s
    ExplicitImports                            |    4      2      6    39.3s
      no_implicit_imports                      |           1      1     7.1s
      all_qualified_accesses_are_public        |           1      1     4.7s
ERROR: Package ModelingToolkitBase errored during testing

The two findings were the implicitly imported UnPack binding and Julia 1.11's missing public metadata for the documented Base.Iterators.filter, map, and reverse APIs.

Passing after

The same command passes with this PR:

Test Summary: | Pass  Total     Time
JET Tests     |   54     54  4m02.7s

Test Summary: | Pass  Total     Time
Aqua Tests    |   21     21  5m21.7s
571.292962 seconds (412.98 M allocations: 20.602 GiB, 3.46% gc time, 31.16% compilation time: 8% of which was recompilation)
     Testing ModelingToolkitBase tests passed

What changed

UnPack and @unpack are now explicitly imported while retaining the existing reexport. The three documented iterator APIs are recorded in the existing qualified-access compatibility list because Julia 1.11 does not declare them public; Julia 1.12 does.

This addresses the Julia 1.11 findings exposed by #4989 without changing the iterator implementations or runtime behavior.

Additional verification

~/.juliaup/bin/julia +1.11 --project=../.runic-env -e 'using Runic; exit(Runic.main(ARGS))' -- --check --diff lib/ModelingToolkitBase/src/ModelingToolkitBase.jl lib/ModelingToolkitBase/test/qa/aqua.jl
typos lib/ModelingToolkitBase/src/ModelingToolkitBase.jl lib/ModelingToolkitBase/test/qa/aqua.jl
git diff --check

All three commands exited successfully with no findings.

No documentation or public API changed, so the documentation build was not run. Test groups outside ModelingToolkitBase_QA were not run.

Ignore this PR until it has been reviewed by @ChrisRackauckas.

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https://chatgpt.com/codex/tasks/01a03a17-ad6f-7131-82fc-d0fd57ea6512