fix: use SPDX license identifier 'Apache-2.0' instead of ambiguous 'Apache' (#3814)
The `license` field in `setup.py` is set to `"Apache"`, which is
ambiguous — it does not map to a recognized SPDX license identifier.
PyPI surfaces this value as-is in the package JSON metadata, making it
difficult for automated license compliance tools to identify the actual
license.
The repository's LICENSE file is the Apache License, Version 2.0, so
the correct SPDX identifier is `Apache-2.0`.
This change updates the `license` field from `"Apache"` to
`"Apache-2.0"` so that PyPI metadata unambiguously reflects the
project's license.
References:
- SPDX License List: https://spdx.org/licenses/Apache-2.0.html
- PEP 639 (license metadata): https://peps.python.org/pep-0639/