Replace parallel EC GET with paired stream

[cthulhu-rider]

this approach seems more cost-effective overall. However, basic load tests did not show any increase in throughput. Therefore lets resolve this issue separately

[codecov]

Codecov Report

❌ Patch coverage is 5.43580% with 1009 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.80%. Comparing base (84ededb) to head (087994b).

Files with missing lines	Patch %	Lines
pkg/services/object/get.go	2.55%	720 Missing and 5 partials ⚠️
pkg/services/object/get/ec.go	2.31%	167 Missing and 2 partials ⚠️
pkg/services/object/proto.go	0.00%	46 Missing ⚠️
pkg/services/object/server.go	41.17%	19 Missing and 1 partial ⚠️
pkg/network/cache/clients.go	40.90%	13 Missing ⚠️
internal/object/wire.go	40.00%	9 Missing ⚠️
internal/protobuf/seekers.go	0.00%	8 Missing ⚠️
pkg/services/object/util.go	33.33%	5 Missing and 3 partials ⚠️
pkg/services/object/get/service.go	0.00%	5 Missing ⚠️
pkg/services/object/get/util.go	0.00%	3 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3998      +/-   ##
==========================================
- Coverage   28.33%   27.80%   -0.54%     
==========================================
  Files         681      681              
  Lines       45753    46763    +1010     
==========================================
+ Hits        12964    13002      +38     
- Misses      31556    32524     +968     
- Partials     1233     1237       +4     

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[roman-khimov]

OK, let's postpone this to 0.54.0 then.