yaml float handling

[ggmarshall]

Annoying thing in pyyaml where 5e-6 would be read in as a str instead of a float, seems to be fixed but no release yet see: yaml/pyyaml#555 , this just adds a custom writer to add the decimal point so floats will be read correctly, maybe a better way to handle this though

[gipert]

a unit test would be easy and useful also for the future...

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.60%. Comparing base (8df6472) to head (81c3451).
Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dbetto/utils.py	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   83.10%   91.60%   +8.49%     
==========================================
  Files           6        6              
  Lines         444      536      +92     
==========================================
+ Hits          369      491     +122     
+ Misses         75       45      -30     

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