Fix out-of-place DAEProblem solve; make the test suite actually run

[ChrisRackauckas-Claude]

Please ignore until reviewed by @ChrisRackauckas. Draft.

Source fix: out-of-place DAEProblem was broken

The out-of-place branch of the common-interface solve (src/common.jl) wired the residual as a 2-arg ODE RHS:

f = (t, u) -> prob.f(u, p, t)        # wrong: DAE residual is not f(u, p, t)

But an out-of-place DAEProblem's residual is 4-arg (du, u, p, t), and the solver calls the residual with (t, u, du). So every out-of-place DAE errored (MethodError, the 2-arg lambda can't take the solver's 3 args). Mirror the in-place wiring (F! = (out, t, u, du) -> prob.f(out, du, u, p, t)):

f = (t, u, du) -> prob.f(du, u, p, t)

test/common.jl only exercised the in-place prob_dae_resrob, so this path had no coverage. Added a non-MTK out-of-place index-1 DAE regression test (u1' = -u1, 0 = u1 - u2; exact u1 = u2 = exp(-t)) that errors without the fix.

Test infrastructure: the suite ran zero tests in CI

runtests.jl used GROUP = get(ENV, "GROUP", "all"), but the CI/downgrade workflow exports GROUP="" (empty, not unset). get returns "", so both the core and QA guards were false — CI ran zero tests yet reported success. Coerced an empty GROUP to "all".

Alloc tests: fix a measurement artifact (not a loosen)

Once the suite actually ran, three @allocated == 0 assertions in alloc_tests.jl surfaced as failures (dassl_norm, get_history_t!, get_history_y!). These are measurement artifacts of measuring @allocated at non-const global testset scope: a Float64 return gets boxed (16 B) and escape analysis can't elide a returned view's SubArray wrapper (48 B). Measured inside a function barrier (typed-local args, direct call) all three allocate 0. The == 0 guard is preserved — a real view→copy regression still allocates a fresh array (≥80 B) inside the barrier and is still caught.

Verification (local, Julia 1.10, Pkg.test)

Testing maxorder                   |  36   36
Testing common interface           |   4    4   <- new OOP DAE regression test
DAE Initialization                 |  10   10
ModelingToolkit DAE Initialization |  46   46   <- was 45 + 1 error before the fix
Interface Compatibility            |  12   12
Convergence tests                  |  20   20
In-Place Operations                |  36   36
QA                                 |  20   20   <- was 17 + 3 failed before
Testing DASSL tests passed   (exit 0)

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