Analyzer to prevent duplicate function names

### Description

If you create two functions, say in two different files, but give them the same name, your build process will succeed, but you'll get a runtime failure. We should be able to catch this at build time.

No source files, tests, or entry points are named. Start by locating the build-time analyzer or function-discovery entry point and review existing validation tests. Done means duplicate function names across files are reported during the build instead of causing only a runtime failure.

Written by the indexing model from the issue text.