Add nullspace accuracy parameter

[bvenn]

Related issue

closes #194

Please list the changes introduced in this PR

• remove LinearAlgebraService requirement for nullspace calculation
• add optional accuracy parameter for matrix rank determination

Description

The accuracy parameter defines the threshold that separates zero singular values from nonzero ones. The default threshold is set to 1e-08.

let a = matrix [[..]
let ns = LinearAlgebra.nullspace(Accuracy=1e-10)
let product = a * ns
//product should give matrix of zeros`

[Required] please make sure you checked that

• [x] The project builds without problems on your machine

[Optional]

• [x] Added unit tests regarding the added features