Support recursive source dependencies for run dependencies

[Hofer-Julian]

Similar to #2814, but it is both less complex and brings less value.

If we look at out tutorial, we find that the Python package depends on the C++ package (python_bindings) during runtime. It would be good to be able to just add the python_bindings to the run-dependencies:

pixi/docs/source_files/pixi_projects/pixi_build_workspace/pixi.toml

Line 29 in 944b3e9

[package.run-dependencies]

Until this issue is fixed, one has to add it manually to the environment

pixi/docs/source_files/pixi_projects/pixi_build_workspace/pixi.toml

Lines 10 to 12 in 944b3e9

	[dependencies]
	python_bindings = { path = "packages/python_bindings" }
	rich_example = { path = "." }