in the files in MeshToolsLib.

 to MeshToolsLib

IMHO makes the application code more readable.

The fmt library happily accepts std::string without
any conversions.

Include spdlog via BaseLib/Logging.h, which
provides macro replacements for
ERR/DBUG/WARN/INFO...

Move variables around, constify.

Avoid copying of the id_map: take a reference.

The code after the bounds calculation relies on special
values in the bounds pair in the case of absent MaterialIDs.
This is now separated in own lambda.

Clang format run on near-the-header lines.

Happy New Year

Especially on iterator types and 'new' allocations.