fix: Preserve spaces in string list options

[yuefdev]

The benchmark and validation example wrappers pass --example_args through ListOption<std::string>. A value such as --image=/tmp/test images/sample.ppm,--threads=2 currently truncates the image argument to --image=/tmp/test because formatted string extraction stops at whitespace.

Specialize string-list parsing to preserve each comma-delimited item, including spaces and tabs. Keep numeric parsing and the existing append, empty-input, trailing-comma, and empty-item behavior. Add six cases to the existing UNIT suite; the header guard is normalized by the repository hook.

Validation:

• Compiled and ran the six case bodies in a standalone MSVC C++14 host harness: three cases fail before the fix, all six pass afterward and on this independent main-based branch.
• Compiled the actual UNIT source against the repository test-framework headers. The full Arm validation executable was not built or run; the host compile reports existing warnings from shared headers.
• All contributor hooks pass when combined locally with the Windows tooling fixes in fix: Make contributor checks work on Windows #1310. This PR contains only the ListOption header and UNIT test, with no dependency on that PR.