fix(rewards): apply collateral in repo allocation

[Desel72]

Summary

Applies finalized open-PR collateral when collecting repo-local PR allocation scores, so contributors with collateral are allocated from merged earned_score - same-repo collateral_score clamped at zero.

This keeps no-collateral allocation proportional to merged PR scores while making repo-bounded emission allocation agree with the collateral-adjusted scoring output.

Related Issues

Fixes #1266

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Testing

• Tests added/updated
• Manually tested

uv run pytest tests/validator/test_blend_emission_pools.py -q
uv run ruff check gittensor/validator/emission_allocation.py tests/validator/test_blend_emission_pools.py
uv run ruff format --check gittensor/validator/emission_allocation.py tests/validator/test_blend_emission_pools.py

Checklist

• Code follows project style guidelines
• Self-review completed
• Changes are documented (if applicable)