33 feat detect duplicate else if conditions as unreachable branches

[SizzleUnrlsd]

We added a new analysis pass that detects duplicate else if conditions that are logically unreachable. The analyzer now emits a DuplicateIfCondition warning with precise source locations. This was integrated into the diagnostics pipeline, added to the error-code enum, and wired into the build. We also added a set of diagnostic test cases covering positive detections (including commuted operands and nested scenarios) and negative cases (distinct conditions and separate if blocks).

Architecture rationale: we implemented this as its own analysis module and hooked it into the existing analysis pipeline rather than embedding the logic inside the main analyzer. This keeps responsibilities separated, makes the check independently testable, and avoids coupling with other diagnostics. Using dominator information and a lightweight source check balances precision with implementation cost, reducing false positives without requiring full AST-level parsing