[Epic] Add declarative configuration for common packaging tasks (resolver, sdist, modification) #936

As of today, Fromager does not have declarative configuration options to solve problems like building a package from a git clone, resolving packages on Github / Gitlab, or structured patching. These are common tasks that currently require a Python plugin. In downstream, we have over 60 plugins. The majority of plugins are trivial and only deal with GitLabTagProvider, git clone, and some simple patching.

Some ideas:

Resolver

• resolve on PyPI
• resolve with GitHubTagProvider
• resolve with GitLabTagProvider

Download / sdist

• download sdist from PyPI
• download tarball from URL
• git clone
• download artifact from GitHub / GitLab release
• build sdist with PEP 517

Patching

• apply patch from file
• modify pyproject.toml build system requirement
• version-specific pyproject.toml patching (e.g. only >-1.0,<1.1)
• replace / delete line in a file (like Ansible's lineinfile)
• fix sdist PKG-INFO
• remove an install requirement from sdist metadata and wheel metadata (requires-dist field)
• align install requirement with build environment (e.g. if package was built with Torch 2.9.1, force dependency on exactly Torch 2.9.1)