chore: migrate /ccu-info to new v1/user-info API

[hjjackyang]

Why? Colab is in the process of deprecating old /tun/m/* APIs. This PR migrates getCcuInfo (also renamed to getConsumptionUserInfo) from /ccu-info to new v1/user-info API with get_ccu_consumption_info=true.

Demo screencast showing GPU/TPU selector still working and new API calls logged with status 200.

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There are 2 optimizations as part of this migration:

1. assignServer used to call both getSubscriptionTier and getCcuInfo to retrieve server descriptors. After this migration, we can get everything we need to assign a server from the basic getUserInfo call, reducing 2 HTTP calls to one.
2. ConsumptionNotifier used to call getSubscriptionTier while it already has access to a ConsumptionUserInfo instance via event emitter. After this migration, we can directly get subscription tier from ConsumptionUserInfo without needing to call getUserInfo again, removing the redundant HTTP call.

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Internal tracking bug: b/485350944

[colaboratory-team]

Oh my, thanks for such a massive change for the migration. Hope it wasn't too bad. I can only say my review was cursory at best, and I depend on the passing tests. I believe this will be also soon used for integration tests (Kokoro?) and hit the real sandbox endpoints soon? Thanks again!

[hosungs]

Oops, reviewed/approved as colaboratory-team, may not matter, but just in case, approving as hosungs too. :) Thanks again!

[hjjackyang]

@hosungs - Thanks for the quick review!

I believe this will be also soon used for integration tests (Kokoro?) and hit the real sandbox endpoints soon?

Actually, our E2E tests run as part of this PR pre-merge checks, and they hit real production endpoints I believe:
https://github.com/googlecolab/colab-vscode/actions/runs/22204531648/job/64225543737?pr=432

So rest assured!

[amtoney524]

lgtm - really nice refactor on top of the migration!! thanks Jack!