Add custom reprs to awkward coordinate classes

[Saransh-cpp]

Closes #209

• Add custom __repr__ methods
• Update the doctests to reflect the same

[codecov-commenter]

Codecov Report

Merging #212 (63976f5) into main (ba4e8b4) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
- Coverage   82.45%   82.43%   -0.02%     
==========================================
  Files          96       96              
  Lines       10388    10394       +6     
==========================================
+ Hits         8565     8568       +3     
- Misses       1823     1826       +3     

Impacted Files	Coverage Δ
src/vector/backends/awkward.py	75.89% <50.00%> (-0.22%)	⬇️

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[henryiii]

Switch to f-strings, slightly faster and cleaner, otherwise good!