Feat: Class-based solvers

[mrava87]

This PR creates class-based solvers following PyLops' pylops.optimization.basesolver.Solver base class.

As part of this effort, all function-based solvers are modified to have the same set of tolerances exposed to the users:

• tol: tolerance on objective function change between iterations (as (cost_previous - cost_current ) / cost_previous < too directly handled in the step method
• rtol: relative tolerance on objective function vs initial value (handled as callback)
• xtol: absolute tolerance on change of solution - this is currently parked as requires a new PyLops release that fixes https://github.com/PyLops/pylops/pull/762/changes. This will simply require adding

  if xtol is not None:
       callbacks.append(ModuleUpdateCallback(xtol))
  

  to each function based solver.

Note that as part of this, a breaking change is made on PPXA and ConsensusADMM which previously used tol to check for the solution change.

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 high

Alerts:
⚠ 1 issue (≤ 0 issues of at least minor severity)

Results:
1 new issue

Category	Results
ErrorProne	1 high

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🟢 Metrics -82 complexity · 5 duplication

Metric	Results
Complexity	-82
Duplication	5

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