Rename CLI command to canpy #39

Preserve backwards compatibility after the rename to canpy. Retain a
codeanalyzer console script that prints a one-line deprecation notice to stderr
(so piped stdout stays clean) and then runs the CLI unchanged. To be removed in a
future release.

Scope:

• codeanalyzer/main.py: deprecated_main() shim
• pyproject [project.scripts]: codeanalyzer -> deprecated_main