Add two missing CI features

[hildebrandmw]

These features correspond to two recently added entries in diskann-benchmark that missed updating the CI feature set. The type aliases in the diskann-benchmark/src/index/bftree/* are in response to clippy lints now running on that code.

[Copilot]

Pull request overview

Updates the CI feature set to cover recently added diskann-benchmark feature-gated benchmarks, and refactors BfTree streaming benchmark function signatures to satisfy clippy lints now that clippy runs on that code.

Changes:

• Add multi-vector and bftree to the DISKANN_FEATURES list used by CI and nightly clippy/test jobs.
• Introduce local type aliases to simplify complex tuple return types in BfTree streaming benchmark helpers (clippy type_complexity mitigation).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
diskann-benchmark/src/index/bftree/spherical_streaming.rs	Adds a tuple type alias and uses it as the helper return type to reduce signature complexity.
diskann-benchmark/src/index/bftree/full_precision_streaming.rs	Adds a generic tuple type alias and uses it as the helper return type to reduce signature complexity.
.github/workflows/nightly.yml	Adds multi-vector and bftree to the feature list exercised by nightly jobs.
.github/workflows/ci.yml	Adds multi-vector and bftree to the feature list exercised by PR CI jobs.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.47%. Comparing base (9c66b5e) to head (162a8f9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1272      +/-   ##
==========================================
- Coverage   91.50%   90.47%   -1.03%     
==========================================
  Files         498      498              
  Lines       95522    95522              
==========================================
- Hits        87408    86427     -981     
- Misses       8114     9095     +981     

Flag	Coverage Δ
miri	90.47% <ø> (-1.03%)	⬇️
unittests	90.14% <ø> (-1.33%)	⬇️

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see 39 files with indirect coverage changes

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