refactor: implement AbstractMiner class for hathor simulator

[glevco]

Acceptance Criteria:

• Create AbstractMiner class
• Rename MinerSimulator to GeometricMiner and inherit from AbstractMiner

[codecov]

Codecov Report

Merging #564 (ad12395) into master (4ce0568) will increase coverage by 0.00%.
The diff coverage is 98.27%.

@@           Coverage Diff           @@
##           master     #564   +/-   ##
=======================================
  Coverage   83.37%   83.38%           
=======================================
  Files         214      215    +1     
  Lines       18959    18972   +13     
  Branches     2614     2614           
=======================================
+ Hits        15808    15819   +11     
- Misses       2580     2581    +1     
- Partials      571      572    +1     

Impacted Files	Coverage Δ
hathor/simulator/__init__.py	100.00% <ø> (ø)
hathor/simulator/miner/abstract_miner.py	96.55% <96.55%> (ø)
hathor/simulator/miner/geometric_miner.py	100.00% <100.00%> (ø)
hathor/simulator/simulator.py	92.61% <100.00%> (ø)

... and 1 file with indirect coverage changes

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