Improve buffers sizes and buffer size computation

[sschaetz]

Description

When using fast-cpp-csv-parser in a project with -Wall -Werror I am hitting two issues that this PR works around:

• incorrect size computation in strncpy
• buffer sizes too small for the long paths I see when working with bazel

[ben-strasser]

The larger error message numbers are now on master.

[ben-strasser]

The strncpy change does not actually change anything as a null-char is added on the next line.