RCBC-554: Add support for search score fusion

[DemetrisChr]

Motivation

As part of SDK API 3.11 support we are adding the new Scoring API which enables configuring score fusion for a hybrid FTS query.

Changes

• Deprecate SearchOptions#disable_scoring
• Add SearchOptions#scoring which can accept three types of scoring
  • Couchbase::SearchScoring::SearchScoringNone
    • should be used instead of SearchOptions#disable_scoring
    • cannot be set if SearchOptions#disable_scoring is set to True
  • Couchbase::SearchScoring::SearchScoringRelativeScoreFusion (Stability uncommitted)
  • Couchbase::SearchScoring::SearchScoringReciprocalRankFusion (Stability uncommitted)
• Updated the FIT protocol mirror
• Added support for score fusion in the FIT performer
• Raise FeatureNotAvailable if score fusion is used with couchbase2

Results

Score fusion FIT tests pass

[Copilot]

🟢 Approval recommended

The only unresolved finding is a non-blocking documentation nit.

Pull request overview

Adds search score-fusion support across the Ruby API, native backend, Protostellar layer, and FIT performer.

Changes:

• Adds none, reciprocal-rank, and relative-score scoring modes.
• Validates deprecated disable_scoring interactions and transport support.
• Updates FIT protocols, capability mapping, performer logic, and tests.

File summaries

File	Description
test/search_scoring_test.rb	Tests scoring modes, validation, and compatibility.
lib/couchbase/search_options.rb	Defines scoring strategies.
lib/couchbase/protostellar/request_generator/search.rb	Maps supported scoring and rejects unsupported fusion.
lib/couchbase/options.rb	Adds scoring options and conflict validation.
fit-performer/proto/shared.exceptions.proto	Synchronizes replica exceptions.
fit-performer/proto/sdk.workload.proto	Synchronizes replica commands.
fit-performer/proto/sdk.search.proto	Adds scoring messages and options.
fit-performer/proto/sdk.kv.replicas.proto	Defines replica strategies.
fit-performer/proto/sdk.kv.options.proto	Defines replica options.
fit-performer/proto/sdk.kv.commands.proto	Defines replica command payloads.
fit-performer/proto/sdk.cluster.query.index_manager.proto	Removes an unused import.
fit-performer/proto/sdk.caps.proto	Adds score-fusion and replica capabilities.
fit-performer/proto/.clang-format	Excludes mirrored schemas from formatting.
fit-performer/lib/fit/performer/service.rb	Advertises score-fusion support.
fit-performer/lib/fit/performer/commands/search/search_query_command.rb	Applies scoring to legacy search queries.
fit-performer/lib/fit/performer/commands/search/search_command.rb	Applies scoring to search requests.
fit-performer/lib/fit/performer/commands/search/options_builder.rb	Converts FIT scoring options.
ext/rcb_search.cxx	Maps scoring into native requests.

Nit: In lib/couchbase/search_options.rb:1340, use the actual public type name SearchScoringNone instead of ScoringNone in the documentation.

Review details

• Files reviewed: 19/19 changed files
• Comments generated: 1
• Review effort level: Balanced

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