feat: allow multiple authors in poetry init

[YNan-varamor]

Summary

Allows poetry init --author to be passed multiple times, e.g.:

poetry init --author "Alice Example <alice@example.com>" --author "Bob Example <bob@example.com>"

Why

Fixes #8864. The issue asks for a non-interactive way to provide multiple authors. A maintainer suggested supporting repeated --author flags, which keeps the CLI usable in scripts and avoids interactive prompts.

Changes

• Marks the init command's --author option as repeatable
• Validates every provided author with the existing author validator
• Writes multiple authors to [project].authors while preserving the existing single-author interactive/default behavior
• Adds a regression test for repeated --author

Validation

• python -m pytest tests/console/commands/test_init.py::test_init_non_interactive_with_multiple_authors tests/console/commands/test_init.py::test_init_non_interactive_existing_pyproject_add_dependency -q -o addopts=''
• git diff --check

AI assistance disclosure

This PR was prepared with assistance from OpenAI Codex. The change was reviewed locally and validated with focused tests.