fix density fidelity

[codecov[bot]]

Codecov Report

Merging #392 (ae13810) into master (c073d7e) will increase coverage by 0.04%. The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master     #392      +/-   ##
==========================================
+ Coverage   88.72%   88.77%   +0.04%     
==========================================
  Files          73       73              
  Lines        4347     4357      +10     
==========================================
+ Hits         3857     3868      +11     
+ Misses        490      489       -1     

Impacted Files	Coverage Δ
src/EasyBuild/block_extension/FSimGate.jl	68.42% <0.00%> (-3.81%)	:arrow_down:
src/EasyBuild/qft_circuit.jl	100.00% <ø> (ø)
lib/YaoArrayRegister/src/utils.jl	85.86% <100.00%> (+1.20%)	:arrow_up:
lib/YaoBlocks/src/abstract_block.jl	88.77% <100.00%> (ø)
lib/YaoBlocks/src/composite/chain.jl	95.41% <100.00%> (ø)
lib/YaoBlocks/src/utils.jl	94.87% <100.00%> (+0.13%)	:arrow_up:
src/EasyBuild/google53.jl	74.60% <100.00%> (+0.40%)	:arrow_up:
src/EasyBuild/variational_circuit.jl	97.77% <100.00%> (+0.10%)	:arrow_up:
... and 1 more

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[GiggleLiu]

Hi, I feel there are some other issues related to fidelity needs to be fixed so I opened a new PR #393 . I find the fidelity obtained use the sqrt function has very low precision, the one in the new PR might give better precision.