SplitStore: supress compaction near upgrades

[vyzo]

This adds the necessary logic to suppress compaction near upgrades and avoid issues with garbage collection of migrated state; see #7565

[codecov]

Codecov Report

Merging #7734 (489782e) into master (9331714) will decrease coverage by 0.01%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master    #7734      +/-   ##
==========================================
- Coverage   39.58%   39.57%   -0.02%     
==========================================
  Files         640      640              
  Lines       68332    68350      +18     
==========================================
- Hits        27052    27051       -1     
- Misses      36647    36657      +10     
- Partials     4633     4642       +9     

Impacted Files	Coverage Δ
node/modules/chain.go	76.00% <0.00%> (ø)
blockstore/splitstore/splitstore.go	26.87% <100.00%> (+3.00%)	⬆️
blockstore/splitstore/splitstore_compact.go	51.76% <100.00%> (+0.65%)	⬆️
chain/stmgr/execute.go	86.95% <0.00%> (-4.35%)	⬇️
node/hello/hello.go	63.63% <0.00%> (-3.41%)	⬇️
chain/sub/incoming.go	54.43% <0.00%> (-3.38%)	⬇️
miner/miner.go	55.62% <0.00%> (-2.99%)	⬇️
chain/events/events_height.go	68.90% <0.00%> (-2.53%)	⬇️
blockstore/buffered.go	40.00% <0.00%> (-2.23%)	⬇️
chain/stmgr/searchwait.go	66.02% <0.00%> (-1.29%)	⬇️
... and 21 more

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