Manager: Check registry cache immediately during discovery

[mkykadir]

to reduce Registry load. Even this might directly block the discovery task (Registry might not have records cached yet), this condition is expected to mostly happen during node initialization.

[codecov[bot]]

Codecov Report

Merging #3304 (3df8e00) into v0.x.x (be9b8d1) will increase coverage by 1.23%. The diff coverage is 70.00%.

@@            Coverage Diff             @@
##           v0.x.x    #3304      +/-   ##
==========================================
+ Coverage   87.83%   89.07%   +1.23%     
==========================================
  Files         164      165       +1     
  Lines       16964    17072     +108     
==========================================
+ Hits        14901    15207     +306     
+ Misses       2063     1865     -198     

Flag	Coverage Δ
integration	34.32% <70.00%> (?)
unittests	87.82% <70.00%> (-0.02%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
source/agora/network/Manager.d	78.98% <70.00%> (+1.76%)	:arrow_up:
source/agora/common/Task.d	88.88% <0.00%> (-11.12%)	:arrow_down:
source/agora/test/NetworkDiscovery.d	84.09% <0.00%> (-4.55%)	:arrow_down:
source/agora/node/Validator.d	91.45% <0.00%> (-0.47%)	:arrow_down:
source/agora/flash/Node.d	80.67% <0.00%> (-0.43%)	:arrow_down:
source/agora/consensus/state/Ledger.d	89.18% <0.00%> (-0.33%)	:arrow_down:
source/agora/node/main.d	44.85% <0.00%> (ø)
source/agora/consensus/protocol/Nominator.d	92.18% <0.00%> (+0.53%)	:arrow_up:
source/agora/test/ValidatorRecurringEnrollment.d	95.19% <0.00%> (+0.96%)	:arrow_up:
... and 9 more

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