Reject zero benchmark resamples on the command line

Description

--benchmark-resamples=0 currently parses successfully, even though the bootstrap analysis needs a nonempty set of resamples. Reject zero at the command-line boundary, mirroring the existing validation of --benchmark-samples.

Use parseUInt to validate the value before updating ConfigData, and report a specific error for malformed input. Add command-line regressions for zero and nonnumeric input, retain the existing positive-value test, document the constraint, and update the SelfTest approval baselines. No amalgamated files are changed.

Validation on Windows with Clang 23.1.3/libc++, C++14, and the basic-tests development preset:

• Before the fix, the new zero-value test fails because parsing succeeds; the malformed-value test fails because the parser returns the generic conversion error.
• After the fix, the command-line group passes all 263 assertions in 4 test cases.
• All 82 CTest entries pass, including approval tests after regenerating and reviewing the expected output with tools/scripts/approve.py.
• Linux, macOS, and sanitizer builds were not run locally.

GitHub Issues

No linked issue; this change is limited to command-line validation of the resample count.