Modernize packaging

[cdce8p]

• Move project metadata from setup.py to pyproject.toml
• Use SPDX license identifier PEP 639.
• Bump min Python version to 3.9. Required for setuptools v77, the first release with support for SPDX license expressions.

Metadata diff

 ...
-Author: Brett Adams
-Author-email: hello@teslemetry.com
+Author-email: Brett Adams <hello@teslemetry.com>
+License-Expression: Apache-2.0
-Home-page: https://github.com/Teslemetry/teslemetry_stream
+Project-URL: Source code, https://github.com/Teslemetry/teslemetry_stream
 ...
-Classifier: License :: OSI Approved :: Apache Software License
 ...
-Requires-Python: >=3.8
+Requires-Python: >=3.9
 ...