Writecache fixes

[fyrchik]

There are 2 problems with the current flush logic:

1. Objects are evicted from the cache even if PUT to the main storage failed.
2. There is a race condition, so that where an object could be silently evicted from LRU without removal from the storage.

In this PR we change this logic in 2 aspects:

1. Removing evicted items is done in the eviction callback.
2. The removal itself is done in batches to avoid blocking client threads.

[codecov]

Codecov Report

Merging #1745 (36df737) into master (180e5e9) will increase coverage by 0.01%.
The diff coverage is 43.37%.

@@            Coverage Diff             @@
##           master    #1745      +/-   ##
==========================================
+ Coverage   33.16%   33.18%   +0.01%     
==========================================
  Files         351      350       -1     
  Lines       23384    23411      +27     
==========================================
+ Hits         7756     7768      +12     
- Misses      14984    14992       +8     
- Partials      644      651       +7     

Impacted Files	Coverage Δ
cmd/neofs-adm/internal/modules/morph/initialize.go	0.00% <0.00%> (ø)
pkg/local_object_storage/shard/delete.go	69.04% <0.00%> (ø)
pkg/local_object_storage/shard/head.go	70.58% <0.00%> (ø)
pkg/local_object_storage/writecache/flush.go	23.01% <0.00%> (+0.35%)	⬆️
pkg/local_object_storage/writecache/options.go	28.57% <ø> (+4.18%)	⬆️
pkg/local_object_storage/writecache/storage.go	28.16% <3.03%> (+3.77%)	⬆️
...ct_storage/blobstor/blobovniczatree/blobovnicza.go	60.75% <62.50%> (-12.93%)	⬇️
...object_storage/blobstor/blobovniczatree/control.go	68.49% <78.26%> (-0.36%)	⬇️
pkg/local_object_storage/shard/get.go	77.96% <100.00%> (ø)
pkg/local_object_storage/writecache/state.go	33.33% <100.00%> (-1.97%)	⬇️
... and 9 more

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