chore: implement yaml settings inheritance

[glevco]

Acceptance Criteria

• Implement new deep_merge() dict utils function
• Implement new validated_named_tuple_from_dict() utils function
• Implement new dict_from_extended_yaml() utils function, allowing parsing of extensible yaml files
• Improve dict_from_yaml() utils function, adding error handling
• Update HathorSettings parsing to use new utils functions

This change resolves #614. Now, yaml settings support an inheritance mechanism that can be used to create custom configurations by changing just a subset of settings attributes.

For example, in the hathor/conf/my_network.yml file:

extends: mainnet.yml

NETWORK_NAME: my_network

Then, if this file is set in --config-yaml or HATHOR_CONFIG_YAML, settings would behave exactly like mainnet settings, and only the NETWORK_NAME would be changed. Changing specific nested attributes is also supported.

Both relative and absolute file paths are supported (relative from the yaml file location, or from a custom root if the custom_root arg is set).

[codecov]

Codecov Report

Merging #618 (17eacb2) into master (d7508e0) will increase coverage by 0.14%.
The diff coverage is 97.51%.

❗ Current head 17eacb2 differs from pull request most recent head 688c29b. Consider uploading reports for the commit 688c29b to get more accurate results

@@            Coverage Diff             @@
##           master     #618      +/-   ##
==========================================
+ Coverage   83.63%   83.78%   +0.14%     
==========================================
  Files         232      238       +6     
  Lines       19826    19990     +164     
  Branches     2714     2735      +21     
==========================================
+ Hits        16582    16749     +167     
+ Misses       2644     2642       -2     
+ Partials      600      599       -1     

Impacted Files	Coverage Δ
hathor/manager.py	70.60% <0.00%> (-0.05%)	⬇️
hathor/builder/cli_builder.py	70.27% <40.00%> (-0.16%)	⬇️
hathor/conf/settings.py	97.05% <93.33%> (-0.05%)	⬇️
hathor/event/event_manager.py	90.74% <100.00%> (ø)
hathor/event/model/event_data.py	100.00% <100.00%> (ø)
hathor/event/storage/event_storage.py	100.00% <100.00%> (ø)
hathor/event/storage/memory_storage.py	100.00% <100.00%> (ø)
hathor/event/storage/rocksdb_storage.py	94.18% <100.00%> (+0.28%)	⬆️
hathor/event/websocket/request.py	100.00% <100.00%> (ø)
hathor/exception.py	100.00% <100.00%> (ø)
... and 8 more

... and 2 files with indirect coverage changes