update_verifier: verify blocks in parallel

This CL is to change update_verifier to verify blocks in parallel to
maximize storage bandwidth, it also preallocate the buffer to avoid
vector allocation within reading loop.

Test:
care_map.txt:
system
16,0,517,556,32770,33084,98306,98620,163842,164156,229378,229692,294914,295228,483544,524288,524296
vendor
8,0,119,135,32770,32831,96150,98304,98306

With CL:
init: Service 'update_verifier_nonencrypted' (pid 711) exited with status 0 waiting took 2.978424 seconds

Without CL:
init: Service 'update_verifier_nonencrypted' (pid 695) exited with status 0 waiting took 4.466320 seconds

Bug: 63686531
Test: reboot with manual insert care_map.txt
Change-Id: Idf791865f15f6ff6cad89bf7ff230ee46c6adccc