[WIP] Multi-Step Methods

[avik-pal]

TODOs

• [x] PotraPtak3
• [ ] SinghSharma
  • [ ] 4
  • [ ] 5
  • [ ] 7
• [ ] Tests
• [ ] Documentation
• [ ] Handle tuple/namedtuple caches in @internal_caches

[codecov[bot]]

Codecov Report

Attention: 107 lines in your changes are missing coverage. Please review.

Comparison is base (8f9a432) 58.65% compared to head (75f1874) 57.12%.

Files	Patch %	Lines
src/descent/multistep.jl	7.01%	53 Missing :warning:
src/core/approximate_jacobian.jl	43.75%	18 Missing :warning:
src/abstract_types.jl	0.00%	14 Missing :warning:
src/internal/helpers.jl	38.88%	11 Missing :warning:
src/core/generalized_first_order.jl	81.25%	6 Missing :warning:
src/algorithms/multistep.jl	0.00%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #356 +/- ## ========================================== - Coverage 58.65% 57.12% -1.53% ========================================== Files 44 47 +3 Lines 2612 2708 +96 ========================================== + Hits 1532 1547 +15 - Misses 1080 1161 +81 ```

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