Reject malformed MaxConnections values in TelnetAppender configuration

[jmestwa-coder]

Summary

This patch hardens integer configuration parsing for TelnetAppender by rejecting malformed and out-of-range numeric values before they reach allocation-sensitive logic.

Previously, OptionConverter::toInt() relied on atol() narrowing behavior, which could silently accept overflowed, underflowed, or partially parsed values.

Changes

• replace atol() narrowing in OptionConverter::toInt() with bounded strtoll() parsing

• reject:

  • overflow values
  • underflow values
  • empty input
  • partial numeric parses

• preserve valid integer parsing behavior

• reject negative MaxConnections values before resize logic

• remove signed/unsigned resize comparison hazards in TelnetAppender

Tests

Added regression coverage for:

• malformed numeric input rejection
• overflow and underflow handling
• valid integer boundary parsing
• TelnetAppender configuration fallback behavior