Brev 9032/Use Nebius Capacity Advisor to determine GPU instance availability

[kirtiip20]

Problem

Nebius GPU instance types showed as available in the Brev UI based on tenant quota alone, even when Nebius had no on-demand capacity in that region. Users could select such a type (e.g. 8× H200, L40s) and the launch would then fail at provisioning time.

Root cause
Availability was computed only from tenant quota allowances, with no check against the provider's actual capacity. A tenant can hold quota in a region where Nebius currently has no capacity available so the type was still marked available and failed on launch.

Fix
Integrated the Nebius Capacity Advisor (ResourceAdvice) API so availability reflects real-time on-demand capacity & tenant quota:

1. Fetch Capacity Advisor data during each instance-type synchronization and build a region:platform:preset availability map (getResourceAdviceMap, buildResourceAdviceMapFromItems).
2. Updated GPU availability resolution (resolvePresetAvailability) to require:Available capacity from Capacity Advisor, and
   Remaining tenant quota.
   Treated DATA_STATE_UNKNOWN and AVAILABILITY_LEVEL_LIMIT_REACHED as unavailable capacity
3. If the Capacity Advisor API is fully unavailable, degrade gracefully to quota-only (logged as a warning) so the catalog doesn't go blank.
4. Upgraded github.com/nebius/gosdk to v0.2.22, which includes support for the Capacity Advisor API.

[drewmalin]

Can we move this to the test file as this is only used there?

[kirtiip20]

Sure, moved buildResourceAdviceMapFromItems from instancetype.go to test file.

[drewmalin]

Let's err on the side of no named returns (instead of (key string, available uint32, ok bool), just use (string, uint32, bool))

[kirtiip20]

Updated resourceAdviceEntry to use no named return types (string, uint32, bool) instead of named returns.

[drewmalin]

Minor but it might be nice to just hand the capacity lookup key here directly, rather than the individual components that will only be used to build the key.

[kirtiip20]

Updated, The call site now constructs the key once using capacityAdviceKey(location.Name, platform.Metadata.Name, preset.Name) and passes it directly, and resolvePresetAvailability now accepts a capacityKey string instead of individual region, platform, and preset components.