Improve throughput of float formatting

[robomics]

On my machine this gives a 4-5% performance boost when running e.g. hictk dump file.cool --normalization weight > /dev/null.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.55%. Comparing base (f98dc1b) to head (9bca695).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #311   +/-   ##
=======================================
  Coverage   77.55%   77.55%           
=======================================
  Files         173      173           
  Lines       21225    21225           
  Branches     2310     2310           
=======================================
  Hits        16462    16462           
- Misses       3756     3757    +1     
+ Partials     1007     1006    -1     

Flag	Coverage Δ
[tests	integration](https://app.codecov.io/gh/paulsengroup/hictk/pull/311/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=paulsengroup)	67.99% <ø> (-0.01%)
[tests	unittests](https://app.codecov.io/gh/paulsengroup/hictk/pull/311/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=paulsengroup)	75.89% <ø> (+0.01%)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.