all: fix pypi name

[tsubakiky]

This pull request updates the project name from connect-py to connectpy across the codebase and documentation to ensure consistency and avoid potential issues with naming conventions. The key changes include updates to installation instructions, dependency references, metadata, and user agent strings.

Documentation updates:

• Updated the installation command in README.md to use connectpy instead of connect-py.
• Updated references to connectpy in the contribution section of README.md.

Dependency and configuration updates:

• Replaced connect-py with connectpy in the dependencies and source paths in conformance/pyproject.toml.
• Updated examples/pyproject.toml to use connectpy in dependencies and source paths.
• Changed the project name to connectpy in pyproject.toml.

Code updates:

• Updated the DEFAULT_CONNECT_USER_AGENT string in src/connect/protocol_connect/constants.py to reflect the new project name.
• Updated the DEFAULT_GRPC_USER_AGENT string in src/connect/protocol_grpc/constants.py to use connectpy.