Enhance contract to support keyword arguments during reduction

[jofrevalles]

Summary

Following from the PR #31, this PR modifies the contract(tensors...) function to support kwargs, therefore allowing them to be passed to the contract(tensor1, tensor2) function.

This change is useful since Tenet.contract(expr::EinExpr) calls the contract method with the dims keyword argument, leading to an error due to the absence of handling kwargs in the contract(tensors...) function.

With this update, the dims argument (as well as other potential keyword arguments) can be appropriately handled during the tensor contraction process.

[codecov]

Codecov Report

Merging #32 (e7cd1dc) into master (fdcb1d7) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #32   +/-   ##
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  Coverage   82.98%   82.98%           
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  Files           6        6           
  Lines         241      241           
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  Hits          200      200           
  Misses         41       41           

Impacted Files	Coverage Δ
src/Numerics.jl	88.13% <100.00%> (ø)