feat!: enforce all rerankers always return relevance score & deprecate linear combination fixes (#1687)

- Enforce all rerankers always return _relevance_score. This was already
loosely done in tests before but based on user feedback its better to
always have _relevance_score present in all reranked results
- Deprecate LinearCombinationReranker in docs. And also fix a case where
it would not return _relevance_score if one result set was missing

docs/src/reranking/linear_combination.md

@@ -1,6 +1,9 @@
 # Linear Combination Reranker
 
-This is the default re-ranker used by LanceDB hybrid search. It combines the results of semantic and full-text search using a linear combination of the scores. The weights for the linear combination can be specified. It defaults to 0.7, i.e, 70% weight for semantic search and 30% weight for full-text search.
+!!! note
+    This is depricated. It is recommended to use the `RRFReranker` instead, if you want to use a score based reranker.
+
+It combines the results of semantic and full-text search using a linear combination of the scores. The weights for the linear combination can be specified. It defaults to 0.7, i.e, 70% weight for semantic search and 30% weight for full-text search.
 
 !!! note
     Supported Query Types: Hybrid

docs/src/reranking/rrf.md

@@ -1,6 +1,6 @@
 # Reciprocal Rank Fusion Reranker
 
-Reciprocal Rank Fusion (RRF) is an algorithm that evaluates the search scores by leveraging the positions/rank of the documents. The implementation follows this [paper](https://plg.uwaterloo.ca/~gvcormac/cormacksigir09-rrf.pdf).
+This is the default re-ranker used by LanceDB hybrid search. Reciprocal Rank Fusion (RRF) is an algorithm that evaluates the search scores by leveraging the positions/rank of the documents. The implementation follows this [paper](https://plg.uwaterloo.ca/~gvcormac/cormacksigir09-rrf.pdf).
 
 
 !!! note