refactor(builder): Change HathorManager.__init__ and change tests to use TestBuilder

[msbrogli]

Acceptance criteria

1. Make parameters peer_id, tx_storage, and network required on HathorManager.__init__(...).
2. Create a TestBuilder to build all objects for tests.
3. Refactor tests to use TestBuilder.

Note: I was considering to refactor CliBuilder to use Builder but I felt it was too much for now. Besides that, I don't need to change the CliBuilder to move forward with my project.

[codecov]

Codecov Report

Merging #559 (1f84f43) into dev (f7ef8a7) will increase coverage by 0.04%.
The diff coverage is 91.91%.

❗ Current head 1f84f43 differs from pull request most recent head 7b2dd3c. Consider uploading reports for the commit 7b2dd3c to get more accurate results

@@            Coverage Diff             @@
##              dev     #559      +/-   ##
==========================================
+ Coverage   83.30%   83.35%   +0.04%     
==========================================
  Files         212      214       +2     
  Lines       18729    18959     +230     
  Branches     2596     2614      +18     
==========================================
+ Hits        15603    15803     +200     
- Misses       2561     2582      +21     
- Partials      565      574       +9     

Impacted Files	Coverage Δ
hathor/simulator/simulator.py	92.61% <ø> (ø)
hathor/builder/builder.py	91.70% <91.70%> (ø)
hathor/builder/__init__.py	100.00% <100.00%> (ø)
hathor/builder/cli_builder.py	79.19% <100.00%> (ø)
hathor/manager.py	70.73% <100.00%> (-0.38%)	⬇️

... and 4 files with indirect coverage changes

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[jansegre]

Functionally I'm more than OK with this PR, I really like the direction we're going with the Builder. I only have some smaller naming and behavior suggestions.

[glevco]

Like Jan, I like this direction and I only have minor comments. Moving CliBuilder to this solution soon would be great.