prevent peers from spamming block parts

[pompon0]

If a node is even just 1 block behind, his peers will start to spam random block parts at him which

• saturates the network
• kicks out other msgs from the outbound queue (because block parts are the highest priority messages)
• OOMs the node - it is unable to process all the incoming parts and the parts are large.
  All this behavior was observed on a 50-node 1-region cluster with 1000txs/s (with lifted limits on the block size).

Fix boils down to properly marking the block parts as sent, so that they are not retransmitted indefinitely.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 57.25%. Comparing base (02c9462) to head (442257a).

Files with missing lines	Patch %	Lines
internal/consensus/reactor.go	50.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #318      +/-   ##
==========================================
- Coverage   57.31%   57.25%   -0.07%     
==========================================
  Files         257      257              
  Lines       34597    34599       +2     
==========================================
- Hits        19829    19808      -21     
- Misses      13180    13204      +24     
+ Partials     1588     1587       -1     

Files with missing lines	Coverage Δ
internal/consensus/reactor.go	57.27% <50.00%> (-1.75%)	⬇️

... and 6 files with indirect coverage changes

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