Do not add default ports for explicit hosts

[lin-hongkuan]

Summary

Stop _parse_host from appending :80 or :443 when the input already includes an explicit http:// or https:// scheme without a port.

Motivation

When callers configure a custom host such as https://example.com, the client currently normalizes it to https://example.com:443. That changes the visible configured host and can be problematic for reverse proxies or environments that expect the default port to remain implicit.

Fixes #222

Changes

• Track whether the input included an explicit scheme.
• Preserve the existing Ollama default port :11434 for bare hosts.
• Avoid adding default HTTP/HTTPS ports for explicit scheme hosts without a port.
• Add doctest examples and a parametrized regression test.

Testing

• uv run --with pytest --with pytest-anyio --with pytest-httpserver pytest tests/test_client.py::test_parse_host_default_ports --doctest-modules ollama/_client.py → 8 passed in 0.64s
• uv run --with pytest --with pytest-anyio --with pytest-httpserver pytest tests/test_client.py::test_parse_host_default_ports --doctest-modules ollama/_client.py tests/test_client.py → 80 passed in 3.29s
• uv run --with ruff ruff check ollama/_client.py tests/test_client.py → All checks passed!
• git diff --check
• Secret scan on diff: clean