[WIP] Refactor Tests

[MaxenceGollier]

@dpo @MohamedLaghdafHABIBOULLAH, related to #130.

This is very much WIP, but you can already take a look.
I did a proof of concept with R2N, all solvers will eventually have similar tests.

• There should be one function that does most of the test, this function is test-solver.jl
• each solver should have its own test file
• allocations test don't need to be separated from the other tests
• Just testing if the algorithm completes on the bpdn problem is not sufficient
• having verbose > 0 adds too much information/noise into the test results

[MaxenceGollier]

LSR1 is allocating, will try to fix in LinearOperators.jl

[MohamedLaghdafHABIBOULLAH]

Thank you @MaxenceGollier very thoughtful, having the algorithms tested on different problems (toys, bpdn and others) will be very useful!