Add isblk alloced and free_blk_now api in dataservice.

[sanebay]

During replay nublocks needs to check if blks are alloced and call free_blk_now to directly free the blks from bitmap cache and not depend on cp flush.

This PR is needed for eBay/HomeBlocks#144. Details are there in that PR. We cant write UT to repro but its reproduced with long running.
test_volume_io --gtest_filter="VolumeIOTest.LongRunningRandomIO" --num_restarts=4 --num_vols=32 --write_num_io=300 --read_num_io=300 --dev_size_mb=1024000 --log_mods blkalloc:debug --run_time=300

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 15.78947% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.23%. Comparing base (1a0cef8) to head (dbd118e).
⚠️ Report is 311 commits behind head on master.

Files with missing lines	Patch %	Lines
src/lib/blkdata_svc/blkdata_service.cpp	0.00%	11 Missing ⚠️
src/lib/device/virtual_dev.cpp	42.85%	0 Missing and 4 partials ⚠️
src/lib/blkalloc/bitmap_blk_allocator.cpp	0.00%	0 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #826      +/-   ##
==========================================
- Coverage   56.51%   48.23%   -8.28%     
==========================================
  Files         108      110       +2     
  Lines       10300    12855    +2555     
  Branches     1402     6170    +4768     
==========================================
+ Hits         5821     6201     +380     
+ Misses       3894     2565    -1329     
- Partials      585     4089    +3504     

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[shosseinimotlagh]

Please explain the problem thoroughly (with an example and UT command to verify) in the pr comment and how this pr solves the problem.

[sanebay]

Please explain the problem thoroughly (with an example and UT command to verify) in the pr comment and how this pr solves the problem.

This PR is needed for eBay/HomeBlocks#144. Details are there in that PR. We cant write UT to repro but its reproduced with long running.
test_volume_io --gtest_filter="VolumeIOTest.LongRunningRandomIO" --num_restarts=4 --num_vols=32 --write_num_io=300 --read_num_io=300 --dev_size_mb=1024000 --log_mods blkalloc:debug --run_time=300