Add Variable.ZerosBridge

[blegat]

Extracted from #759

[codecov-io]

Codecov Report

Merging #817 into master will increase coverage by 1.89%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master     #817      +/-   ##
==========================================
+ Coverage   90.84%   92.74%   +1.89%     
==========================================
  Files          66       67       +1     
  Lines        7431     7474      +43     
==========================================
+ Hits         6751     6932     +181     
+ Misses        680      542     -138

Impacted Files	Coverage Δ
src/Bridges/Variable/Variable.jl	100% <ø> (ø)	⬆️
src/Bridges/bridge_optimizer.jl	74.01% <50%> (+11.8%)	⬆️
src/Bridges/Variable/zeros.jl	75% <75%> (ø)
src/Bridges/lazy_bridge_optimizer.jl	60.41% <0%> (-4.76%)	⬇️
src/Utilities/functions.jl	94.86% <0%> (+0.34%)	⬆️
src/Bridges/Variable/bridge.jl	25% <0%> (+25%)	⬆️
src/Bridges/Variable/single_bridge_optimizer.jl	33.33% <0%> (+33.33%)	⬆️
src/Bridges/Variable/map.jl	96.92% <0%> (+85.47%)	⬆️

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