cast to Float64 directly instead of using float

[SobhanMP]

Does this make sense?

Closes #515

julia> using SparseArrays, ForwardDiff, LinearAlgebra
julia> A = ForwardDiff.Dual.(sprand(10, 10, 0.1));
julia> qr(A)
ERROR: MethodError: no method matching Float64(::ForwardDiff.Dual{Nothing, Float64, 0})
The type `Float64` exists, but no method is defined for this combination of argument types when trying to construct it.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 84.26%. Comparing base (a5e95ec) to head (0c8f8f3).

Files	Patch %	Lines
src/solvers/spqr.jl	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #521 +/- ## ======================================= Coverage 84.26% 84.26% ======================================= Files 12 12 Lines 9122 9122 ======================================= Hits 7687 7687 Misses 1435 1435 ```

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[rayegun]

What happens in the complex case?

[SobhanMP]

What happens in the complex case?

The same as it used to do.