Density matrix implementation

[GiggleLiu]

• partial_tr
• expect
• probs
• measure
• instruct!
• UnitaryChannel
• zero_state_like
• algebra +, -, *, /
• inplace algebra regscale!, regadd!, regsub!

[codecov]

Codecov Report

Merging #394 (88c1a8b) into master (c073d7e) will increase coverage by 0.18%.
The diff coverage is 99.29%.

@@            Coverage Diff             @@
##           master     #394      +/-   ##
==========================================
+ Coverage   88.72%   88.91%   +0.18%     
==========================================
  Files          73       73              
  Lines        4347     4448     +101     
==========================================
+ Hits         3857     3955      +98     
- Misses        490      493       +3     

Impacted Files	Coverage Δ
lib/YaoBlocks/src/blocktools.jl	84.28% <ø> (ø)
lib/YaoBlocks/src/composite/control.jl	97.95% <ø> (ø)
lib/YaoBlocks/src/composite/kron.jl	95.12% <ø> (ø)
lib/YaoBlocks/src/composite/put_block.jl	100.00% <ø> (ø)
lib/YaoBlocks/src/composite/repeated.jl	100.00% <ø> (ø)
lib/YaoBlocks/src/composite/subroutine.jl	97.22% <ø> (ø)
lib/YaoBlocks/src/composite/tag/dagger.jl	86.36% <ø> (ø)
lib/YaoBlocks/src/primitive/identity_gate.jl	71.42% <ø> (ø)
lib/YaoBlocks/src/primitive/phase_gate.jl	95.00% <ø> (ø)
lib/YaoBlocks/src/primitive/shift_gate.jl	90.00% <ø> (ø)
... and 25 more

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[GiggleLiu]

@Roger-luo I removed the method for applying a UnitaryChannel on ArrayReg to avoid confusing. Otherwise register and density matrix can have different outputs.