[enhancement] Spot heuristics module

There are some situations where we can not use data for calculate odds:

• Recently we found out due to #593 some (all?) opt-in regions from AWS do not offer SpotPlacementScore data, can not find if that will be supported at any time. As so those regions are directly discarded from spot calculations.

• On top of this, from time to time we also miss Eviction metric from Azure due to some unknown issues on their graphql service. In that case we use directly price info.

• Also on some previous research other providers do not support such metric.

This issue proposes to create a generic heuristic module to emulate the score so it can be used on those cases were we will not be able to retrieve that data:

Actual Data

The proposed solution will calculate the score based on the formula

discount = 1 - (spot_price / on_demand_price)

Temporal data

When possible data formula could be improved with temporal data:

Compute deltas or ratios:

delta1d = (current - yesterday) / yesterday

delta7d = (current - lastWeek) / lastWeek

Use those deltas as extra signals:

If the current price is much lower than historical → maybe surplus capacity (good).

If much higher or spiking vs history → maybe risk of interruption (bad).

@anjannath WDYT?

No files, tests, or entry points are named. Start by reviewing the existing AWS SpotPlacementScore and Azure eviction/price handling, along with issue #593, then determine where a provider-neutral heuristic belongs. Done should mean the proposed discount formula can cover cases where spot metrics are unavailable; temporal signals remain an optional design point.