Avoid invalid simplification with conflict markers (#15041)
Previously, `simplify_conflict_markers` assumed that it can remove all
conflict set together, when we need to look at each conflict set
individually. Specifically, `(platform_machine == 'x86_64' and extra ==
'extra-5-foo-b') or extra == 'extra-5-foo-a'` can't be reduced
`platform_machine == 'x86_64'` only because it reduces to true when both
conflict extras are activated.
This case applied in https://github.com/astral-sh/uv/issues/14805, where
a jax 0.5.3 version was used for `platform_machine != 'aarch64' or
sys_platform != 'linux'` and the conflict extra `cu128`, but jax 0.7.0
for the conflict extra `cpu`.
Only removing the faulty inference regresses lockfiles to much more
verbose markers. To balance the much more conservative inference, I
added `unify_inference_sets` to simplify cases where all conflict
branches reduce to the same marker.
This still regresses some markers. For example `sys_platform == 'win32'`
regresses to `sys_platform == 'win32' or (extra == 'extra-3-pkg-x1' and
extra == 'extra-3-pkg-x2')` in `extra_inferences`, even through x1 and
x2 conflict and the second conjunction could be simplified away.
Fixes https://github.com/astral-sh/uv/issues/14805
