Localize coindex in GetInterfaceName to prevent variable leakage

[lwJi]

Motivation

• Prevent accidental leakage or reuse of the loop index coindex when generating interface names, which could cause incorrect output or cross-contamination of state during code generation.

Description

• Add coindex to the Module local variables in GetInterfaceName inside src/BackendCommon.wl, so the index is properly localized during the Do loop.

Testing

• No automated tests were run for this change.

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Codex Task