Add size method to Circuit trait

[moCello]

This change also removes the need to preallocate the circuit builder which in turn removes the need to pass the public parameters when compressing a circuit.

Resolves #767

[codecov]

Codecov Report

Merging #768 (577738b) into master (bcb31de) will decrease coverage by 0.21%.
The diff coverage is 70.00%.

❗ Current head 577738b differs from pull request most recent head 0e0b3d4. Consider uploading reports for the commit 0e0b3d4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #768      +/-   ##
==========================================
- Coverage   85.07%   84.86%   -0.21%     
==========================================
  Files          57       57              
  Lines        4327     4327              
==========================================
- Hits         3681     3672       -9     
- Misses        646      655       +9     

Files	Coverage Δ
src/composer/builder.rs	80.00% <100.00%> (ø)
tests/composer.rs	95.91% <ø> (ø)
src/composer/compiler.rs	98.42% <75.00%> (+0.47%)	⬆️
src/composer/compiler/compress.rs	87.82% <87.50%> (-0.08%)	⬇️
src/composer.rs	91.00% <77.77%> (-0.03%)	⬇️
src/debugger.rs	67.41% <33.33%> (-5.85%)	⬇️
src/runtime.rs	18.75% <0.00%> (-19.72%)	⬇️

... and 4 files with indirect coverage changes

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[ureeves]

LGTM