Introduce a separate crate for integration tests

[stadust]

This speeds up compilation as well as run time, since now all integration tests are compiled into the same binary, as opposed to one binary per test file

[codecov-commenter]

Codecov Report

Merging #71 (b14598e) into master (af4c2ed) will decrease coverage by 0.02%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   17.05%   17.03%   -0.03%     
==========================================
  Files         115      115              
  Lines        8284     8283       -1     
==========================================
- Hits         1413     1411       -2     
- Misses       6871     6872       +1     

Impacted Files	Coverage Δ
pointercrate-demonlist-pages/src/overview.rs	0.00% <ø> (ø)
pointercrate-demonlist/src/record/get.rs	0.00% <ø> (ø)
pointercrate-demonlist/src/record/mod.rs	44.15% <ø> (+1.29%)	:arrow_up:
pointercrate-demonlist/src/record/post.rs	53.45% <ø> (ø)
pointercrate-integrate/src/gd.rs	0.53% <0.00%> (+<0.01%)	:arrow_up:
pointercrate-user-pages/src/account/users.rs	0.00% <0.00%> (ø)
pointercrate-core/src/pool.rs	96.29% <100.00%> (ø)
pointercrate-user-api/src/auth.rs	43.84% <100.00%> (ø)
pointercrate-user/src/auth/mod.rs	90.98% <100.00%> (ø)
pointercrate-demonlist/src/player/claim/put.rs	82.60% <0.00%> (-13.05%)	:arrow_down:
... and 1 more

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