Fix: Mark classes as internal

[localheinz]

This PR

• marks classes as internal to allow modifications without the need for a major release

💁‍♂ Besides, nobody would want to use these classes directly anyway.

[codecov]

Codecov Report

Merging #270 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             master   #270   +/-   ##
=======================================
  Coverage        80%    80%           
  Complexity       39     39           
=======================================
  Files             3      3           
  Lines           175    175           
=======================================
  Hits            140    140           
  Misses           35     35

Impacted Files	Coverage Δ	Complexity Δ
src/Command/NormalizeCommand.php	88.07% <ø> (ø)	32 <0> (ø)	⬇️
src/Command/SchemaUriResolver.php	0% <ø> (ø)	4 <0> (ø)	⬇️

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