support constraints for transient dependencies?

[bollwyvl]

elevator pitch

Add the concept of constraints for controlling resolution of transient dependencies.

motivation

For a number of use cases, constraints help achieve reproducible environments
with more familiar tools and data than the still-prickly pyodide-lock.json.

design ideas

For parity with the positional dependencies, this would likely be a list of PEP-508 specs which get normalized, either up-front affecting all future solves, or in a one-off install:

micropip.set_constraints(["maybe-transient-dep==1.2.3"])

await micropip.install(
    ["direct-dep"], 
    constraints=[
        "another-transient-dep==4.5.6",
        "yet-another-transient-dep@https://example.com/yet_another_transient_dep.py3-none-any.whl",
    ]
)

In an outer build environment, the output of pip list --format=freeze could provide any "interesting" dependencies to something that should work in the browser, even if they need to be slightly tweaked to avoid any emscripten- or pyodide-specific .whl.

[hoodmane]

+1 for this. I like set_constraints better.

[bollwyvl]

Started this up: #177