Add 1D DGMulti GaussSBP solver (supercedes #1930)

[jlchan]

GaussSBP solvers previously were only implemented in 2D and 3D. This PR adds 1D capabilities (using that sum factorization just reduces to mul! in 1D).

Closes #1930

[github-actions[bot]]

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.11%. Comparing base (abf8a08) to head (091fa2d). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1932 +/- ## ========================================== + Coverage 96.10% 96.11% +0.01% ========================================== Files 451 451 Lines 36241 36261 +20 ========================================== + Hits 34826 34850 +24 + Misses 1415 1411 -4 ``` | [Flag](https://app.codecov.io/gh/trixi-framework/Trixi.jl/pull/1932/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/trixi-framework/Trixi.jl/pull/1932/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework) | `96.11% <100.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework#carryforward-flags-in-the-pull-request-comment) to find out more.

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