Cleanup Elastic Scaling Checks for FeatureIndex::ElasticScalingMVP

[EleisonC]

Description

This PR addresses issue #6352, which proposes cleaning up the codebase by assuming that the FeatureIndex::ElasticScalingMVP feature is always enabled.

Integration

• Under the handle_active_leaves_update Set elastic_scaling_mvp to true (provisioner)
• Under the construct_per_relay_parent_state Set inject_core_index to true (backing)

Review Notes

• The inject_core_index flag is used to support elastic scaling. When true, the core index is injected into the BackedCandidate, enabling dynamic core allocation and deallocation.
• I removed this check in the backing file since we assume elastic scaling is enabled.

node_features
    .get(FeatureIndex::ElasticScalingMVP as usize)
    .map(|b| *b)
    .unwrap_or(false);

• I removed this check in the provisioner file since we assume elastic scaling is enabled.

request_node_features() 

if !elastic_scaling_mvp && core_count > 1 {
			continue
		}

[EleisonC]

Hey @sandreim. I have opened up this PR for the code refactor issue.
cc: @alindima