Harden UK release manifest retries

[MaxGhenis]

Summary

• refresh compatible model package pins when retrying release manifest creation from an existing draft manifest
• prefer the imported PolicyEngine UK checkout's pyproject.toml version before falling back to installed package metadata
• only skip missing release manifest entries from Hugging Face, while surfacing unexpected download errors

Existing PR check

• Checked open PRs in PolicyEngine/policyengine-uk-data.
• Publish TRACE TRO declarations for UK data releases #335 and Add public transfer artifact manifest #377 both touch release/artifact manifest areas, but neither covers the checkout-version lookup or EntryNotFoundError handling added here.
• Publish TRACE TRO declarations for UK data releases #335 edits nearby release manifest files, so this may need a small conflict resolution depending on merge order.

Validation

• env -u UV_FROZEN uv run --frozen pytest policyengine_uk_data/tests/test_release_manifest.py
• env -u UV_FROZEN uv run --frozen ruff check policyengine_uk_data/utils/data_upload.py policyengine_uk_data/tests/test_release_manifest.py
• env -u UV_FROZEN uv run --frozen ruff format --check policyengine_uk_data/utils/data_upload.py policyengine_uk_data/tests/test_release_manifest.py
• git diff --check