fix decchar handling in writecell() for AbstractFloat

[sara2512]

This PR fixes #1108.

Currently DecFP.Dec64 Floats are not handled correctly. Decimal character is not replaced.

using DecFP
using DataFrames
using CSV
io = IOBuffer() 
CSV.write(io, DataFrame(:a => Dec64(1)); decimal = ',')
String(take!(io))
# "a\n1.0\n"

With the PR in place the result is as expected.

CSV.write(io, DataFrame(:a => Dec64(1)); decimal = ',')
String(take!(io))
# "a\n1,0\n"

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.

Project coverage is 90.47%. Comparing base (80936af) to head (a05e45f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/write.jl	55.55%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1109      +/-   ##
==========================================
+ Coverage   90.27%   90.47%   +0.19%     
==========================================
  Files           9        9              
  Lines        2314     2319       +5     
==========================================
+ Hits         2089     2098       +9     
+ Misses        225      221       -4     

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[quinnj]

Thanks!