fix(minibf): bound UTxO block lookups

[Liona-orph]

Closes #874.

What changed

• replace the unbounded join_all fan-out in the UTxO model loader with a futures stream
• cap concurrent block_meta_by_tx_hash calls at 64 with buffer_unordered
• preserve missing-block and error handling and the existing result collection

Validation

• cargo test -p dolos-minibf --lib (277 passed, 1 ignored)
• cargo fmt --all -- --check
• git diff --check

cargo clippy -p dolos-minibf --lib -- -D warnings is currently blocked by two pre-existing for_kv_map warnings in crates/cardano/src/utxoset.rs and crates/cardano/src/roll/dreps.rs; this PR does not touch those files.

Summary by CodeRabbit

• Performance Improvements
  • Improved the efficiency of block metadata lookups by processing requests asynchronously with controlled concurrency.
  • Preserved existing handling for missing metadata and lookup errors.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 2fb053ae-3cb9-489f-884d-85a5f86d3d43

📥 Commits

Reviewing files that changed from the base of the PR and between 957cb38 and 7382206.

📒 Files selected for processing (1)

• crates/minibf/src/routes/utxos.rs

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📝 Walkthrough

Walkthrough

The UTxO route now performs block metadata lookups through an unordered stream with a maximum concurrency of 64. Missing metadata remains omitted, and lookup errors remain converted to INTERNAL_SERVER_ERROR.

Changes

UTxO block lookup concurrency

Layer / File(s)	Summary
Bounded metadata lookup stream crates/minibf/src/routes/utxos.rs	The route replaces join_all with buffer_unordered(BLOCK_LOOKUP_CONCURRENCY). The concurrency limit is 64. Existing handling for missing metadata and lookup errors remains unchanged.

Estimated code review effort: 2 (Simple) | ~10 minutes

Mergeability Score: ⚪ Minimal · up to 73822

This localized change bounds concurrent UTxO block lookups while preserving existing error and result handling, with relevant tests and formatting checks passing; no actionable merge-blocking risk remains.

Possibly related PRs

• txpipe/dolos#869: Refines the same block metadata lookup logic by replacing join_all with bounded unordered concurrency.

Suggested reviewers: scarmuega, gonzalezzfelipe

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the primary change: bounding minibf UTxO block lookups.
Linked Issues check	✅ Passed	The PR replaces unbounded join_all with buffer_unordered(64) and preserves lookup handling required by issue #874.
Out of Scope Changes check	✅ Passed	The changes are limited to bounded block metadata lookups and preserve existing behavior, with no unrelated modifications.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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