Streams infra + support in egonet

[afender]

• Stream synchronization behavior: switched to per-thread default stream instead of the legacy default stream
• Update raft tag
• EgoNet upgrade to use uvector instead of device_vector
• EgoNet upgrade to execute on a different stream for each seed
• Perf analysis timers/app for EgoNet

Concurrency is limited by the number of available blocks on the device. Thrust-based codes may request a lot of blocks without a way to control this. In practice, smaller graphs leverage concurrency better than larger ones where tasks may end up waiting for available resources.

We may wait on #1407 before reconciling and merging this
Close #957

[codecov-io]

Codecov Report

Merging #1435 (c47818d) into branch-0.19 (369beee) will increase coverage by 0.02%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.19    #1435      +/-   ##
===============================================
+ Coverage        60.72%   60.75%   +0.02%     
===============================================
  Files               70       70              
  Lines             3132     3134       +2     
===============================================
+ Hits              1902     1904       +2     
  Misses            1230     1230              

Impacted Files	Coverage Δ
python/cugraph/utilities/utils.py	71.65% <0.00%> (ø)
python/cugraph/_version.py	44.80% <0.00%> (+0.39%)	⬆️

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[seunghwak]

LGTM except for few small complaints.

[BradReesWork]

rerun tests

[BradReesWork]

@gpucibot merge