Fix vector search metadata serialization

[jotare]

Description

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.11%. Comparing base (5eebea5) to head (cf13a11).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2570      +/-   ##
==========================================
- Coverage   86.22%   86.11%   -0.12%     
==========================================
  Files         376      376              
  Lines       23559    23559              
==========================================
- Hits        20313    20287      -26     
- Misses       3246     3272      +26     

Flag	Coverage Δ
nucliadb	73.51% <ø> (-0.18%)	⬇️
nucliadb-ingest	28.85% <ø> (ø)
nucliadb-reader	24.84% <ø> (ø)
nucliadb-search	37.60% <ø> (-0.02%)	⬇️
nucliadb-standalone	46.85% <ø> (ø)
nucliadb-train	44.94% <ø> (ø)
nucliadb-writer	39.40% <ø> (-0.01%)	⬇️
nucliadb_dataset	55.45% <ø> (ø)
nucliadb_models	85.04% <ø> (ø)
nucliadb_sdk	80.11% <ø> (ø)
nucliadb_sidecar	89.03% <ø> (ø)
nucliadb_telemetry	86.55% <ø> (ø)
nucliadb_utils	84.05% <ø> (ø)

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