Reject trailing characters in StringHelper numeric parsing

[jmestwa-coder]

Summary

Improve StringHelper::toInt and StringHelper::toInt64 to reject malformed numeric input with trailing non-whitespace characters instead of silently accepting partial parses.

Examples of previously accepted input:

• "123abc" → parsed as 123
• "514udp" → parsed as 514

This change now requires the full numeric string to be consumed (excluding trailing whitespace).

Changes

• Added full-consumption validation after std::stoi / std::stoll
• Preserved support for surrounding whitespace and signed values
• Switched to LOG4CXX_ENCODE_CHAR for consistent cross-platform LogString handling
• Added regression tests covering:
  • trailing characters
  • empty input
  • whitespace-only input
  • embedded whitespace
  • signed numbers

Rationale

OptionConverter::toInt already rejects trailing characters using full-string validation. This change aligns StringHelper numeric parsing behavior with the existing strict parsing semantics used elsewhere in the project and avoids silently accepting malformed numeric configuration values.

[swebb2066]

As the failing tests show, this PR breaks existing code that expects trailing non-digits to terminate an integer.

I do not believe this PR adds any value to the code base, especially given that OptionConverter::toInt is available for cases where trailing characters are an error.

[jmestwa-coder]

@swebb2066 , I was treating the behavior difference as an inconsistency, but I understand now that the permissive parsing in StringHelper::toInt is intentional and relied upon by existing code paths.