Enable code coverage with 90% patch requirement for Rust changes

[Copilot]

Enables code coverage in CI and enforces 90% minimum coverage on changed Rust lines. PRs with insufficient coverage of modifications will be blocked.

Changes

• .github/workflows/ci.yml: Uncommented coverage job with --workspace flag (was previously disabled and scoped to specific packages), added fetch-depth: 0 for diff analysis, set fail_ci_if_error: true

• .codecov.yml: Configured patch coverage at 90% threshold with informational: false to block PRs, project coverage remains informational

Requirements

Repository needs CODECOV_TOKEN secret configured (obtain from codecov.io after connecting repo).

Coverage Enforcement

Codecov analyzes PR diffs and calculates coverage for changed lines only. If patch coverage < 90%, the status check fails and blocks merge. Test files, benchmarks, examples, and test_data/ are excluded.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Enable code coverage in .github/workflows/ci.yml</issue_title>
<issue_description>

DiskANN/.github/workflows/ci.yml

Line 163 in f9c6c4b

# name: code coverage

1. Enable code coverage in .github/workflows/ci.yml
2. Block a PR if the Code Coverage of the changed lines (written in Rust) is lower than 90%</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Enable code coverage in .github/workflows/ci.yml #695

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