Add commutator and anticommutator functions

[Krastanov-agent]

Summary

• Add commutator(A, B) function that computes [A, B] = AB - BA
• Add anticommutator(A, B) function that computes {A, B} = AB + BA
• These are fundamental quantum mechanical operations for operator algebra
• Includes comprehensive documentation with examples

New Functions

• commutator(A::AbstractOperator, B::AbstractOperator): Computes the commutator [A, B] = AB - BA
• anticommutator(A::AbstractOperator, B::AbstractOperator): Computes the anticommutator {A, B} = AB + BA

These functions provide essential quantum mechanical operations that are widely used in:

• Quantum mechanics (canonical commutation relations)
• Quantum field theory (anticommutation relations for fermions)
• Quantum error correction
• Hamiltonian simulation

Examples

# Pauli matrix commutators
σx = sigmax()
σy = sigmay()
comm = commutator(σx, σy)  # Returns 2i*σz

# Fermionic anticommutators  
σx = sigmax()
σz = sigmaz()
anticomm = anticommutator(σx, σz)  # Returns zero matrix

Test plan

• Verify commutator function works correctly on example operators
• Test anticommutator function produces expected results
• Check canonical commutation/anticommutation relations hold
• Verify exports work and no name conflicts exist

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.18%. Comparing base (bcf7093) to head (3e68b86).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/linalg.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

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- Coverage   33.25%   33.18%   -0.08%     
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  Files          15       15              
  Lines         442      443       +1     
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  Hits          147      147              
- Misses        295      296       +1     

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