DM-32682: Fix metadata.add fallback code

[timj]

Previously failing to call addLongDouble() never triggered the call to .add()

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Merging #107 (9854ec1) into master (92fb8c8) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   91.24%   91.29%   +0.04%     
==========================================
  Files          36       36              
  Lines        2148     2148              
==========================================
+ Hits         1960     1961       +1     
+ Misses        188      187       -1     

Impacted Files	Coverage Δ
python/lsst/utils/timer.py	96.26% <100.00%> (+0.93%)	⬆️

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