Fix long-range fork density comparison in select_secure_chain

[coldstar1993]

TITLE

Fix long-range fork density comparison in select_secure_chain

Description

Fixes a bug where both tip_density and candidate_density were computed with identical inputs.
Ensures long-range fork decisions compare the candidate chain density against the tip chain density correctly.

Details
The current implementation computes:

tip_density = relative_min_window_density(candidate, tip)
candidate_density = relative_min_window_density(candidate, tip)

This makes both densities identical, causing long‑range fork resolution to always fall back to the tie path and use select_longer_chain, effectively disabling density-based selection.

The fix swaps the arguments for tip_density:

let tip_density = relative_min_window_density(tip, candidate);
let candidate_density = relative_min_window_density(candidate, tip);

This aligns with the intended semantics: compute each chain’s relative density against the other’s slot horizon.

Type of change

• Bug fix

Checklist

• “Hotfix” to testnet, everything else to staging
• Linked to Github Issue
• This change depends on code or research by an external entity
  • Acknowledgements were updated to give credit
• Unit tests added
• This change requires new documentation.
  • Documentation has been added/updated.
• This change is an Optimization
  • Benchmarks added/run
• Has a known issue
  • Link to the open issue addressing it
• If your PR changes the Operator compatibility (Ex: Upgrade prover versions)
  • This PR adds compatibility for operator for both versions and do not change crates/docs/examples
  • This PR updates batcher and docs/examples to the newer version. This requires the operator are already updated to be compatible