(performance): speed up conflict checking by caching canonical names and tightening whitelist construction

[KRRT7]

pip install and pip check spend measurable time in dependency conflict detection. Two low-risk improvements stand out:

• Cache canonicalized dependency names when building package details so later conflict checks can reuse them.
• Make whitelist construction in install conflict checking order-independent while keeping the existing scope limited to the target packages and their direct dependents.\n\nThis should reduce overhead in a common path without broadening conflict detection behavior.

[KassaSana]

Hi, I'm looking into this. I see #14075 already fixed whitelist order-independence — I'll focus on caching canonical names unless there's more needed for the whitelist part. Planning to open a PR soon.

[KRRT7]

@KassaSana awesome! FYI I forgot to link the PR here but #14088

however, please feel free to work on your PR, I made some changes that are on main already that messed up my own PR and benchmarking and havent had time to work on it.

[KassaSana]

Thanks for pointing me to #14088!

I had a local implementation on the same caching approach and confirmed
the whitelist fix is already on main via #14075.

Won't open dup PR. 'll follow #14088 instead. Happy to help
test or dig in if useful.

[KRRT7]

@KassaSana right now I'm focused on another part of the codebase so if you'd like to collab and help me get that PR moving I'd appreciate it!