feat(events): realiable integration during the load phase

[glevco]

Implement changes described in HathorNetwork/rfcs#52

Acceptance Criteria:

• Implement new EventStorage functionality
  • Storage and retrieval of NodeState
  • Storage and retrieval of event queue feature state
  • Clearing events
• Update HathorManager
  • Remove event_storage arg, make event_manager required, and add enable_event_queue
  • Initialization fails if it starts without the event queue feature, and it was enabled in a previous start
  • Handling of LOAD phase events
• Update EventManager to support handling of LOAD phase events
• Remove --x-emit-load-events CLI flag, as it's not necessary anymore in the way events are handled in the LOAD phase
• New bytes_to_int() function in transaction.util

[codecov]

Codecov Report

Merging #555 (75f3d66) into master (b455e74) will increase coverage by 0.04%.
The diff coverage is 89.91%.

@@            Coverage Diff             @@
##           master     #555      +/-   ##
==========================================
+ Coverage   83.63%   83.68%   +0.04%     
==========================================
  Files         230      231       +1     
  Lines       19536    19622      +86     
  Branches     2681     2687       +6     
==========================================
+ Hits        16339    16420      +81     
- Misses       2607     2608       +1     
- Partials      590      594       +4     

Impacted Files	Coverage Δ
hathor/builder/resources_builder.py	94.23% <0.00%> (ø)
hathor/pubsub.py	94.66% <ø> (ø)
hathor/manager.py	70.91% <70.00%> (-0.13%)	⬇️
hathor/builder/builder.py	90.87% <83.33%> (-0.25%)	⬇️
hathor/event/event_manager.py	90.74% <84.61%> (-5.69%)	⬇️
hathor/event/storage/rocksdb_storage.py	93.90% <96.66%> (+2.67%)	⬆️
hathor/builder/cli_builder.py	71.66% <100.00%> (-0.32%)	⬇️
hathor/event/model/node_state.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)
... and 1 more

... and 4 files with indirect coverage changes