Enhancement: Assemble exception messages using sprintf()

[localheinz]

This PR

• assembles exception messages using sprintf()

Follows #1.

[codecov]

Codecov Report

Merging #55 into master will decrease coverage by 0.25%.
The diff coverage is 85.71%.

@@             Coverage Diff              @@
##             master      #55      +/-   ##
============================================
- Coverage     93.78%   93.53%   -0.26%     
  Complexity       80       80              
============================================
  Files             8        8              
  Lines           193      201       +8     
============================================
+ Hits            181      188       +7     
- Misses           12       13       +1     

Impacted Files	Coverage Δ	Complexity Δ
src/FixtureFactory.php	91.11% <81.81%> (-0.56%)	37.00 <0.00> (ø)
src/EntityDef.php	95.23% <100.00%> (+0.23%)	17.00 <0.00> (ø)

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