Prewarming shards: gRPC to vector index

[jotare]

Description

Describe the proposed changes made in this PR.

How was this PR tested?

Describe how you tested this PR.

[javitonino]

Reviewing logic first. If prewarm flag is updated, the SyncMetadata won't get refreshed. We need to tweak SyncMetadata::set so the config is updated if it changes.

[codecov]

Codecov Report

❌ Patch coverage is 73.91304% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.97%. Comparing base (48a50e9) to head (247cd81).

Files with missing lines	Patch %	Lines
nidx/src/api/grpc.rs	0.00%	7 Missing ⚠️
nidx/src/api/shards.rs	76.19%	1 Missing and 4 partials ⚠️
nidx/nidx_vector/src/segment.rs	84.00%	3 Missing and 1 partial ⚠️
nidx/src/metadata/index.rs	83.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3334      +/-   ##
==========================================
- Coverage   86.01%   85.97%   -0.04%     
==========================================
  Files         530      530              
  Lines       43310    43373      +63     
  Branches    12097    12160      +63     
==========================================
+ Hits        37254    37292      +38     
- Misses       5467     5490      +23     
- Partials      589      591       +2     

Flag	Coverage Δ
nidx	79.56% <73.91%> (-0.11%)	⬇️
nucliadb	74.90% <ø> (ø)
nucliadb-ingest	45.48% <ø> (ø)
nucliadb-reader	45.11% <ø> (ø)
nucliadb-search	49.44% <ø> (ø)
nucliadb-standalone	48.35% <ø> (ø)
nucliadb-train	45.90% <ø> (ø)
nucliadb-writer	49.08% <ø> (ø)
nucliadb_dataset	75.80% <ø> (ø)
nucliadb_models	79.73% <ø> (ø)
nucliadb_sdk	85.29% <ø> (ø)
nucliadb_telemetry	82.89% <ø> (ø)
nucliadb_utils	81.61% <ø> (ø)

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