Add Cassandra 5 SAI index and vector search support

[pchlupacek]

Summary

• Add SAI (Storage Attached Index) support: indexBySAI, indexBySAIVector, indexBySAICollection on TableBuilder
• Add ANN vector search: orderByAnn, orderByAnnShared on QueryBuilder with ORDER BY col ANN OF :param
• Add similarity functions: similarityCosine, similarityEuclidean, similarityDotProduct via new CQLFunction2 trait
• Add CONTAINS, CONTAINS_KEY comparisons and byIndexIn for SAI query operators
• Add index migration support: detect missing/removed/changed indexes and generate DROP/CREATE DDL
• CI updated to test against Cassandra 5.0.7

Changes

New types

• CollectionIndexTarget (KEYS/VALUES/ENTRIES/FULL) for SAI collection indexing
• SimilarityFunction (COSINE/DOT_PRODUCT/EUCLIDEAN) enum
• CQLFunction2[I1, I2, O] trait for two-argument CQL functions

QueryBuilder additions

• orderByAnn / orderByAnnShared — ANN vector ordering with type-safe parameter binding
• function2At / function2AtShared — similarity functions in SELECT with shared parameter support
• byIndexIn — col IN :paramList with List[V] parameter type

Migration

• migrateIndexes compares desired vs current indexes from TableMetadata
• Generates DROP INDEX for removed/changed indexes, CREATE INDEX for new/changed indexes

Test plan

• 7 unit tests for SAI index DDL generation (TableBuilderSpec)
• 10 unit tests for ANN/similarity/IN/CONTAINS CQL generation (QueryBuilderSpec)
• 8 integration tests against Cassandra 5.0.7: SAI create, EQ query, range query, ANN OF, ANN with partition key, cosine/euclidean/dot_product similarity (SAISpec)
• 3 integration tests for index migration: add missing, drop removed, recreate on option change (MigrationsSpec)
• All 148 tests pass on Cassandra 5.0.7, all existing tests remain green

[AdamChlupacek]

LGTM