fix(core-blockchain): allow transition to fork from idle

[air1one]

Summary

Allow transition to fork from idle state, as the ForgerMissing event can be triggered while being idle.

Also implement a 10min delay between each potential checkNetworkHealth as when downloading blocks we can trigger a lot of ForgerMissing events.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

Merging #3614 into 2.6 will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.6    #3614      +/-   ##
==========================================
+ Coverage   66.07%   66.08%   +0.01%     
==========================================
  Files         441      441              
  Lines       12506    12511       +5     
  Branches     1716     1717       +1     
==========================================
+ Hits         8263     8268       +5     
  Misses       4210     4210              
  Partials       33       33              

Impacted Files	Coverage Δ
...ackages/core-blockchain/src/machines/blockchain.ts	100.00% <ø> (ø)
packages/core-blockchain/src/blockchain.ts	66.82% <100.00%> (+0.78%)	⬆️

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