Add convenience factory methods for Schema value types to reduce nesting

[oss-amikos]

Summary

Building a Schema object requires 5+ levels of nested builders (Schema → ValueTypes → FloatListConfig → VectorIndexType → VectorIndexConfig → HnswConfig). This deep nesting is the real friction in schema construction — not the builder pattern itself.

Current

Schema schema = Schema.builder()
    .key(Schema.EMBEDDING_KEY, ValueTypes.builder()
        .floatList(FloatListConfig.builder()
            .vectorIndex(VectorIndexType.builder()
                .config(VectorIndexConfig.builder()
                    .hnsw(HnswConfig.builder()
                        .m(16)
                        .constructionEf(200)
                        .build())
                    .build())
                .build())
            .build())
        .build())
    .build();

Proposed

Add mid-level factory methods that flatten common configurations:

// Convenience: single method for the common HNSW case
Schema schema = Schema.builder()
    .embedding(DistanceFunction.COSINE)
    .build();

// With HNSW tuning
Schema schema = Schema.builder()
    .embedding(DistanceFunction.COSINE, hnsw -> hnsw.m(16).constructionEf(200))
    .build();

// With CMEK
Schema schema = Schema.builder()
    .embedding(DistanceFunction.COSINE)
    .cmek(Cmek.gcpKms("projects/.../cryptoKeys/my-key"))
    .build();

Factory methods to add

On ValueTypes:

• static ValueTypes floatWithHnsw(DistanceFunction distance) — default HNSW params
• static ValueTypes floatWithHnsw(DistanceFunction distance, int m, int constructionEf) — tuned HNSW

On Schema.Builder:

• Builder embedding(DistanceFunction distance) — shorthand for the most common schema pattern
• Builder embedding(DistanceFunction distance, Consumer<HnswConfig.Builder> hnsw) — with HNSW tuning

Design notes

• Additive only — deep nested builder API stays for full customization
• Target the 80% case — most schemas just need distance function + optional HNSW tuning
• Don't abstract away CMEK — it's already a single method call (Cmek.gcpKms(...))
• Schema is cloud-only, so this is primarily a DX improvement for Chroma Cloud users

References

• Schema: src/main/java/tech/amikos/chromadb/v2/Schema.java
• ValueTypes, FloatListConfig, VectorIndexType, VectorIndexConfig, HnswConfig — nested builder chain