perf - optimize State witness internal forwarding

[Trisfald]

This is a small optimization for how validators forward SW parts to themselves.

Before, the part owner was doing:

• SW part validation
• forward to itself + other nodes
• SW part validation
• add to good parts

After this change it does:

• SW part validation
• add to good parts
• forward to other nodes

[jancionear]

I think it'd be better to move store_partial_encoded_state_witness after sending the forward message.
Storing is potentially costly (could do reed solomon decoding), so it's better to first forward the message and then do the (potentially) expensive computation, the latency will be better.

[Trisfald]

Yes, I think it makes sense to prioritize other validators before self

[codecov]

Codecov Report

Attention: Patch coverage is 89.65517% with 3 lines in your changes missing coverage. Please review.

Project coverage is 69.52%. Comparing base (2760d76) to head (2dcbc70).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
...alidation/partial_witness/partial_witness_actor.rs	88.88%	1 Missing and 1 partial ⚠️
...nt/src/stateless_validation/chunk_validator/mod.rs	90.90%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #13818   +/-   ##
=======================================
  Coverage   69.52%   69.52%           
=======================================
  Files         960      960           
  Lines      185684   185702   +18     
  Branches   185684   185702   +18     
=======================================
+ Hits       129090   129118   +28     
+ Misses      51482    51473    -9     
+ Partials     5112     5111    -1     

Flag	Coverage Δ
pytests	1.37% <0.00%> (-0.01%)	⬇️
pytests-nightly	1.45% <0.00%> (-0.01%)	⬇️
unittests	69.14% <89.65%> (+<0.01%)	⬆️
unittests-nightly	69.04% <89.65%> (+<0.01%)	⬆️

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