fix: scheduler should check for ready to flush buffers

[giortzisg]

Description

This fixes a CPU spike reported issue. The scheduler should idle on cases where there is no work available, but in the previous implementation the check for having work was checking for non empty buffers.

In the case where logs where appended, the scheduler would constantly check for non ready buffers, consuming resources and causing the CPU to spike.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.78%. Comparing base (03de096) to head (7a419cf).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1143      +/-   ##
==========================================
- Coverage   86.81%   86.78%   -0.04%     
==========================================
  Files          62       62              
  Lines        6092     6092              
==========================================
- Hits         5289     5287       -2     
- Misses        589      590       +1     
- Partials      214      215       +1     

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