[fix] [test] Fix flaky test testPerTopicExpiredStat

[315157973]

Motivation

Large floats may fail to convert because of commas in the string

Modifications

Change to BigDecimal

Verifying this change

• Make sure that the change passes the CI checks.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.64%. Comparing base (e7c2a75) to head (5706f86).
⚠️ Report is 1799 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #22018      +/-   ##
============================================
- Coverage     73.73%   73.64%   -0.09%     
+ Complexity    32536    32497      -39     
============================================
  Files          1863     1863              
  Lines        138816   138816              
  Branches      15217    15217              
============================================
- Hits         102356   102233     -123     
- Misses        28589    28696     +107     
- Partials       7871     7887      +16     

Flag	Coverage Δ
inttests	24.09% <ø> (-0.14%)	⬇️
systests	23.91% <ø> (-0.16%)	⬇️
unittests	72.91% <ø> (-0.10%)	⬇️

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see 59 files with indirect coverage changes

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