test: add tests and big refactor

[tlambert03]

No description provided.

[codecov]

Codecov Report

Merging #5 (c78f7ee) into main (beb3a0e) will increase coverage by 14.35%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             main        #5       +/-   ##
============================================
+ Coverage   85.64%   100.00%   +14.35%     
============================================
  Files           6         7        +1     
  Lines         216       261       +45     
============================================
+ Hits          185       261       +76     
+ Misses         31         0       -31     

Impacted Files	Coverage Δ
src/in_n_out/__init__.py	100.00% <100.00%> (+15.38%)	⬆️
src/in_n_out/_inject.py	100.00% <100.00%> (ø)
src/in_n_out/_processors.py	100.00% <100.00%> (+43.58%)	⬆️
src/in_n_out/_providers.py	100.00% <100.00%> (+31.57%)	⬆️
src/in_n_out/_store.py	100.00% <100.00%> (ø)
src/in_n_out/_util.py	100.00% <100.00%> (ø)

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