feat: add tool.rattler-build overrides and dynamic version resolution

Add two features borrowed from PR #1849:

1. `[tool.rattler-build.*]` overrides in pyproject.toml let users
   customise any section of the generated recipe (context, package,
   source, build, requirements, tests, about). This is especially
   useful for setting the source URL/git, adding compiler build deps,
   or overriding license files.

2. Dynamic version resolution: when `version` is listed in
   `[project].dynamic`, the generator produces Jinja expressions
   for setuptools_scm and hatchling build backends.

https://claude.ai/code/session_01H8oPndn4UDXz1oHjJaE2fm

Author: claude