Your extension module should be named _hello (notice the leading "_").

pyproject.toml:

# ...

[tool.setuptools]
ext-modules = [
  { name = "_hello", sources = ["src/hc/hello.c", "src/hc/hello.i"] }
]

Check:

• [SO]: c program SWIG to python gives 'ImportError: dynamic module does not define init function' (@CristiFati's answer) contains the SWIG related details

• [SO]: How to solve Python-C-API error "This is an issue with the package mentioned above, not pip."? (@CristiFati's answer) contains info about building with SetupTools