Compressible module: boundary faces emit a spurious wave in 9.2.0

With an identical setup.xml and no user routine, the compressible module (constant gamma) gives a correct Sod shock tube in 9.1.0 and a corrupted one in 9.2.0. Both runs are pure first order upwind, all six boundaries are symmetry, and the time step is fixed and identical, so nothing on the input side differs between the two runs.

The corruption is entirely localised at the boundaries. The rarefaction, the contact discontinuity and the shock are unchanged, and agree with the exact Riemann solution in both versions. What 9.2.0 adds is a spurious wave emitted by each wall at the first time step, which then travels into the domain at the local speed of sound (see figure below).

The case is here, if you want to run it as is: [Sod tube](https://github.com/simvia-tech/tutorials-code_saturne/tree/main/30_compressible/Comp_Sod_Tube)

tutorials-code_saturne/30_compressible/Comp_Sod_Tube のリンクされた Sod チューブケースを、同一の setup.xml を使って 9.1.0 と 9.2.0 で実行し、最初のステップの境界挙動を比較します。compressible モジュールの対称境界の処理を追跡します。9.2.0 の実行でスプリアスな壁波が出力されなくなり、正しい Sod 解が維持されれば完了です。

索引モデルが issue の本文から書いたものです。