Clean up compiler warnings and deprecated usage in core build

[SizzleUnrlsd]

This PR cleans up all observed compilation warnings and modernizes a few obsolete usages, with no functional changes expected.

•	Replace sprintf with snprintf to avoid deprecation warnings
•	Remove unused local variables and a no-op #pragma block
•	Migrate from std::auto_ptr to std::unique_ptr
•	Fix a bitwise OR on booleans by switching to ||
•	Remove an unused class member and silence an unused private field

Tests

•	make -C trunk

[tencent-adm]

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