Warn when ignoring urdf links due to small masses or no inertia defined

[aaronchongth]

🦟 Bug fix

Related to #199 and #1007.

Summary

• Promote sdfdbg calls when ignoring urdf links with small masses or no inertia, to sdfwarn
• Make warnings more verbose, whether inertia was not defined, or mass was too small
• Added tests

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1230 (57d3732) into sdf9 (783818a) will increase coverage by 0.08%.
The diff coverage is 100.00%.

❗ Current head 57d3732 differs from pull request most recent head b323657. Consider uploading reports for the commit b323657 to get more accurate results

@@            Coverage Diff             @@
##             sdf9    #1230      +/-   ##
==========================================
+ Coverage   88.35%   88.44%   +0.08%     
==========================================
  Files          63       63              
  Lines       10093    10102       +9     
==========================================
+ Hits         8918     8935      +17     
+ Misses       1175     1167       -8     

Impacted Files	Coverage Δ
src/parser_urdf.cc	85.75% <100.00%> (+0.58%)	⬆️

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[aaronchongth]

Closing to implement changes to sdf12 before considering backporting to sdf9.