Fix: Supabase vectorstore 'SyncRPCFilterRequestBuilder' object has no attribute 'params'

[Yanghojun]

The functions similarity_search_by_vector_with_relevance_scores and
similarity_search_by_vector_returning_embeddings are currently using:

query_builder.params.set("and", f"({postgrest_filter})")

Previously, I encountered an error when calling
query_builder.params.set("limit", k), which was addressed in issue #377.

However, I found that using the params attribute at all may still cause
errors, since the latest Supabase Python client removes the params property
from SyncRPCFilterRequestBuilder.

To ensure compatibility with the updated SDK, I replaced the old params.set(...)
usage with the officially supported builder methods:

query_builder = query_builder.filter("and", f"({postgrest_filter})")
query_builder = query_builder.limit(k)

This change prevents AttributeError exceptions and aligns the implementation
with the current Supabase Python client API.