Use of `LinearAlgebra.eye` differs from `Base.eye`

[juanfung]

See this warning from causal-sims.jl:

┌ Warning: eye(m::Integer) has been deprecated in favor of I and Matrix constructors. For a direct replacement, consider Matrix(1.0I, m, m) or Matrix{Float64}(I, m, m). If Float64 element type is not necessary, consider the shorter Matrix(I, m, m) (with default eltype(I) Bool). │ caller = top-level scope at none:0 └ @ Core none:0

[juanfung]

Duplicate of #13