Preserve caller orderings during preprocessing

Trust-region preprocessing removes constant blocks from parameter
orderings. Solver::Options copies share these objects. Removal therefore
changes the caller's ordering, and a later Solve can reject it.

Copy supplied linear solver and inner iteration orderings before
preprocessing mutates them. Keep automatic ordering creation unchanged.

Add public Solve tests for both supplied orderings. The linear solver
test makes a constant block variable between calls. The inner iteration
test checks caller group membership after both calls.

Tests: focused regressions 2/2 and affected CTest targets 3/3.
Full build passed. Full CTest passed 139/191; 52 bundle tests could
not find source data from the out-of-tree build. Each of those 52 tests
passed with TEST_SRCDIR set to internal/ceres within the checkout.
Tested on arm64 macOS with Apple Clang 21.0.0.

Issue: https://github.com/ceres-solver/ceres-solver/issues/836

Codex used.

Change-Id: Ia0df3722c0905715cf37677621933040d18c1fa6