fix: prevent null byte truncation bypass in SQL injection detection

[PopoviciMarian]

Changes:

• Replace ContextCallback return type (char*) with CallbackResult struct carrying both data pointer and explicit length
• Use malloc+memcpy instead of strdup in GoContextCallback
• Use C.GoStringN instead of C.GoString on the Go side
• Use binary-safe std::string(ptr, len) constructors in all SQL query
  capture handlers (PDO, PDOStatement, mysqli)
• Use binary-safe string construction in ArrayToJson, GetVar, GetBody,
  and GetHeaders to preserve null bytes in user input data

Summary by Aikido

Security Issues: 0	🔍 Quality Issues: 4	Resolved Issues: 0

🐛 Bugfixes

• Made GoContextCallback use malloc+memcpy and return explicit length.
• Used binary-safe std::string(ptr,len) and C.GoStringN to preserve nulls.

🔧 Refactors

• Replaced char* ContextCallback with CallbackResult struct carrying length.
• Added null checks and malloc failure handling to avoid crashes.

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[aikido-pr-checks]

GetVar now constructs and returns a std::string copy for each call, causing a heap allocation and memory copy per call; consider returning a non-owning view or deferring copies to callers.

Details

✨ AI Reasoning
​GetVar was modified to allocate and copy the PHP string into a std::string on every call. The function is used by many higher-level methods (method, URL, headers, etc.), so each call now incurs heap allocation and memory copy. This increases work proportional to the data size per call and multiplies across callers, turning many cheap O(1) pointer accesses into O(n) allocations and copies. Avoidable repeated allocations are an obvious performance regression.

🔧 How do I fix it?
Move constant work outside loops. Use StringBuilder instead of string concatenation in loops. Cache compiled regex patterns. Use hash-based lookups instead of nested loops. Batch database operations instead of N+1 queries.

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