Support pip environment markers

pip requirements specifiers can have "environment markers", i.e. syntax that includes `;`. For example `pywin32; sys_platform = "win32"`. See https://pip.pypa.io/en/stable/reference/requirement-specifiers/

This came up while [we wanted to add](https://github.com/comfyanonymous/ComfyUI/pull/8351) a windows only requirement for adding sandbox to comfy. We're working around for now but adding a tracking bug here to remove the workarounds once it's properly supported by the manager.