feat: allow creating drop message for accumulator

[vaibhavtiwari33]

Closes #357

Testing

Tested with and without message drop semantics.

Disk Usage

When using the drop method the size of the folder where WALs are stored remains roughly constant across time:

/workspace/cws (master)$ kexec accumulator-blackhole-blackhole-0-gjb7u -c numa -- /bin/bash
root@accumulator-blackhole-blackhole-0:/# du -sh /var/numaflow/pbq
2.8M    /var/numaflow/pbq
root@accumulator-blackhole-blackhole-0:/# du -sh /var/numaflow/pbq
2.0M    /var/numaflow/pbq
root@accumulator-blackhole-blackhole-0:/# du -sh /var/numaflow/pbq
2.3M    /var/numaflow/pbq

When not using the drop method and running the loop without awaiting any result, the size steadily increases:

/workspace/cws (master)$ kexec accumulator-empty-blackhole-0-sn8dg -c numa -- /bin/bash
root@accumulator-empty-blackhole-0:/# du -sh /var/numaflow/pbq
7.4M    /var/numaflow/pbq
root@accumulator-empty-blackhole-0:/# du -sh /var/numaflow/pbq
16M     /var/numaflow/pbq
root@accumulator-empty-blackhole-0:/# du -sh /var/numaflow/pbq
33M     /var/numaflow/pbq

Memory Usage

When using the drop method, the memory usage for the numa container in accumulator vertex remains mostly steady

root@accumulator-blackhole-blackhole-0:/# cat /sys/fs/cgroup/memory.current
12353536
root@accumulator-blackhole-blackhole-0:/# cat /sys/fs/cgroup/memory.current
12410880
root@accumulator-blackhole-blackhole-0:/# cat /sys/fs/cgroup/memory.current
12832768
root@accumulator-blackhole-blackhole-0:/# cat /sys/fs/cgroup/memory.current
12922880
root@accumulator-blackhole-blackhole-0:/# cat /sys/fs/cgroup/memory.current
12718080

Without the drop method the memory usage increases quickly

/workspace/cws (master)$ kexec accumulator-empty-blackhole-0-sn8dg -c numa -- /bin/bash
root@accumulator-empty-blackhole-0:/# cat /sys/fs/cgroup/memory.current
186560512
root@accumulator-empty-blackhole-0:/# cat /sys/fs/cgroup/memory.current
201605120
root@accumulator-empty-blackhole-0:/# cat /sys/fs/cgroup/memory.current
205459456
root@accumulator-empty-blackhole-0:/# cat /sys/fs/cgroup/memory.current
220364800
root@accumulator-empty-blackhole-0:/# cat /sys/fs/cgroup/memory.current
283959296

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.74%. Comparing base (e3d3afd) to head (0b8e3e1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #358   +/-   ##
=======================================
  Coverage   92.74%   92.74%           
=======================================
  Files          67       67           
  Lines        3514     3514           
  Branches      228      228           
=======================================
  Hits         3259     3259           
  Misses        190      190           
  Partials       65       65           

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