global: adapt to zstd 1.5.7

All our code changes required to support the upgrade from 1.5.6.

* Rust zstd upgraded to 1.5.7 to match C version.
* Test output changes.
* `zstd_errors.h` inclusion via `zstd.h` caused problems.
* MUSL 1.1 compatibility issues (see previous commit).

Author: bmwiedemann

.github/workflows/sdist.yml

@@ -16,6 +16,7 @@ jobs:
 
       - name: Build sdist
         run: |
+          python -m pip install -r ci/requirements.txt
           python setup.py sdist
 
       - name: Upload sdist