[INFRA] Improve packaging

[eseiler]

• Exclude .git when building source package
• Add tests to all target
• Remove tests target

Dropped

Because the dependencies might also use CPM, we need to keep the source cache.
E.g., when not having cpm in the source cache, seqan3 would try to download it.

• Make CPM not call find_package (Git REQUIRED)
• Exclude use_ccache, CPM source when building source package
• Put robin-hood in contrib
• Replace {CPM,use_ccache}.cmake with fetched scripts when building source package

[seqan-actions]

Documentation preview available at https://docs.seqan.de/preview/seqan/needle/170

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.35%. Comparing base (b73aa47) to head (180aca2).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #170   +/-   ##
=======================================
  Coverage   84.35%   84.35%           
=======================================
  Files           4        4           
  Lines        1138     1138           
  Branches      113      113           
=======================================
  Hits          960      960           
  Misses        178      178           

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