fix: Address input validation vulnerabilities in OCPP message handling

[itsvishalchauhan]

Summary

This PR fixes multiple input validation vulnerabilities that could cause crashes or undefined behavior when processing malformed OCPP messages or server responses.

Vulnerabilities Fixed

High Severity

• MOC-003: NULL pointer dereference in Request/Response parsing
  • Files: Request.cpp, RequestQueue.cpp
  • Fix: Add bounds validation before array access

Medium Severity

• MOC-001: Out-of-bounds read in timestamp fractional second parsing (Time.cpp)
• MOC-004: NULL pointer in TransactionEvent nested JSON access (TransactionEvent.cpp)
• MOC-005: Typo "parenIdTag" → "parentIdTag" (MicroOcpp.cpp)

Low/Informational

• MOC-006: Integer overflow in FTP PASV port calculation (FtpMbedTLS.cpp)
• MOC-007: Integer overflow in configuration parsing (Configuration.cpp, ChangeConfiguration.cpp, VariableService.cpp)
• MOC-002: Unsigned underflow with zero-length certificate serial (CertificateMbedTLS.cpp)

Testing

• All fixes preserve existing behavior for valid inputs
• Invalid inputs now return errors instead of causing crashes

Breaking Changes

None - all fixes are backwards compatible

---

Vulnerabilities identified and remediation proposed by Nebari.ai — AI-native proactive security intelligence solution