feat(vectordb): add Nested Filtering Condition for complex boolean filter logic

[Shinu95J]

This PR adds support for recursive filter nesting in the vectordb package, enabling complex boolean expressions like (A OR B) AND (C OR D) in vector search queries.

Previously, the filter abstraction only supported flat conditions within Must/Should/MustNot clauses. While multiple FilterSets could be combined with AND logic, there was no way to express nested boolean groups like:
(status = "active" OR status = "pending") AND (region = "US" OR region = "EU")
Qdrant natively supports nested filter clauses, and this change exposes that capability through the vectordb abstraction.

Changes

• v1/vectordb/filters.go: Added NestedFilterCondition type that wraps a FilterSet, allowing filters to be used as conditions
• v1/qdrant/converter.go: Added convertVectorDBNestedFilterCondition to handle the new condition type
• v1/vectordb/doc.go: Updated Filter Types table to include NestedFilterCondition
• v1/qdrant/doc.go: Added documentation example for nested filters

// Filter: (status = "active" OR status = "pending") AND (region = "US" OR region = "EU")
filters := []*vectordb.FilterSet{
    vectordb.NewFilterSet(
        vectordb.Must(
            &vectordb.NestedFilterCondition{
                Filter: &vectordb.FilterSet{
                    Should: &vectordb.ConditionSet{
                        Conditions: []vectordb.FilterCondition{
                            vectordb.NewMatch("status", "active"),
                            vectordb.NewMatch("status", "pending"),
                        },
                    },
                },
            },
            &vectordb.NestedFilterCondition{
                Filter: &vectordb.FilterSet{
                    Should: &vectordb.ConditionSet{
                        Conditions: []vectordb.FilterCondition{
                            vectordb.NewMatch("region", "US"),
                            vectordb.NewMatch("region", "EU"),
                        },
                    },
                },
            },
        ),
    ),
}

Example Supported Expressions

Expression	Outer Clause	Inner Clause
(A OR B) AND (C OR D)	Must	Should
(A AND B) OR (C AND D)	Should	Must
(A AND B) AND (C AND D)	Must	Must

[alphamt]

PR was reviewed on another closed PR