Fix #954. safe_memcmp in tinystring.

[kelson42]

This is PR to reintroduce safer memcopy, Unfortunately it seems because of problem with noble (and the compiler) we had to remove it. When all the CI is green (including deb packaging) we could reintroduce it.

See #962

UBSan was complaining about std::memcmp being called with nullptr arguments even when the count == 0. This adds a "safe" wrapper that will just return 0 if the count is 0 or if either of the pointers are nullptr.

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.20%. Comparing base (2f519c7) to head (98021a8).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tools.h	75.00%	0 Missing and 1 partial ⚠️
src/writer/tinyString.h	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #966      +/-   ##
==========================================
+ Coverage   58.13%   58.20%   +0.06%     
==========================================
  Files         101      101              
  Lines        5384     5388       +4     
  Branches     2197     2198       +1     
==========================================
+ Hits         3130     3136       +6     
+ Misses        795      794       -1     
+ Partials     1459     1458       -1     

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