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

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 57.55%. Comparing base (ba2600f) to head (3c73608).

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   57.53%   57.55%   +0.01%     
==========================================
  Files          99       99              
  Lines        4724     4728       +4     
  Branches     1976     1977       +1     
==========================================
+ Hits         2718     2721       +3     
  Misses        704      704              
- Partials     1302     1303       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.