Standardize default configs and add debug configs

[leohenon]

Closes #137

• All *-default configs now use m=16, ef_construction=128
• Added *-debug config for each engine with parallel=1 (upload + search)
• Specialty variants (on-disk, rps, quantization) left unchanged

[Copilot]

Pull request overview

This PR standardizes the “default” HNSW construction parameters across the single-node engine configs and adds new “*-debug” configs to make debugger-driven runs easier by forcing single-threaded upload/search.

Changes:

• Updated each *-default configuration to use the standardized HNSW build settings (m=16, ef_construction=128 in engine-appropriate parameter names).
• Added new *-debug configs per engine with parallel=1 for both upload_params and search_params.
• Left specialty configs (on-disk, RPS, quantization variants) unchanged, per the issue/description.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
experiments/configurations/weaviate-single-node.json	Standardized default index build params; added weaviate-debug with single-threaded upload/search.
experiments/configurations/redis-single-node.json	Standardized default HNSW index params; added redis-debug with single-threaded upload and reduced search parallelism.
experiments/configurations/qdrant-single-node.json	Standardized default hnsw_config; added qdrant-debug with single-threaded upload/search.
experiments/configurations/qdrant-native-single-node.json	Standardized default hnsw_config; added qdrant-native-debug with single-threaded upload/search.
experiments/configurations/pgvector-single-node.json	Added pgvector-debug with single-threaded upload/search while keeping standardized HNSW build params.
experiments/configurations/opensearch-single-node.json	Standardized default ef_construction; added opensearch-debug with single-threaded upload/search.
experiments/configurations/milvus-single-node.json	Standardized default efConstruction; added milvus-debug with single-threaded upload/search.
experiments/configurations/elasticsearch-single-node.json	Standardized default ef_construction; added elasticsearch-debug with single-threaded upload/search.

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