feat: timed field-index creation; bfb create-field-index / drop-field-index

[tellet-q]

Note: base is not dev! Only merge after #158

Add a dedicated sub-command to create payload indices and time the build:

bfb upload --file config.yaml -n 1M --skip-field-indices
bfb create-field-index --file config.yaml --json field-index.json

- Field index creation ---
color (keyword): 0.316 s (server 0.277 s)
price (integer): 0.316 s (server 0.287 s)
Total: 0.632 s

Each index is created with wait=true, so elapsed time reflects the build, not the round-trip. Indices build sequentially, so Total is the cross-run number; to attribute cost to one field, build it alone and re-measure on the same data with the companion drop-field-index:

bfb create-field-index --file config.yaml --field color
bfb drop-field-index   --file config.yaml --field color

Per-field timings land under results.create_field_index. config.num_vectors is now Option — omitted for phase-only commands that neither upload nor query.

[Copilot]

Pull request overview

This PR adds CLI support to create and drop payload field indices after uploading data, capturing per-field wall-clock/server timings and recording them in the JSON results. It also adjusts the results schema so phase-only commands don’t emit a misleading default config.num_vectors, and refactors field-index creation into reusable “spec” builders for both CLI- and YAML-config-driven collection setup.

Changes:

• Add bfb create-field-index / bfb drop-field-index commands and emit per-field timings under results.create_field_index.
• Refactor field-index request construction into pure spec builders and centralize timed creation/drop logic in collection.
• Make config.num_vectors optional and omitted for phase-only commands; update JSON-related tests and docs accordingly.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/results.rs	Adds create_field_index results phase + per-field timing structs; makes config.num_vectors optional and updates tests.
src/main.rs	Wires new subcommands, runs field-index creation with timing + optional index/memory follow-up, and passes num_vectors into results.
src/collection/mod.rs	Implements timed create_field_indices, drop_field_indices, and improves wait_index robustness/progress output.
src/collection/from_config.rs	Exposes field_index_specs_from_config (pure) and reuses the shared timed creation function.
src/collection/from_args.rs	Builds field-index specs from CLI flags (pure) and reuses the shared timed creation function.
src/args/mod.rs	Adds clap subcommands/args for create-field-index and drop-field-index.
src/optimizations.rs	Updates comments/tests to reflect field-index-triggered optimizer work attribution.
README.md	Documents the new commands and clarifies JSON output semantics (one wording issue noted).
DEVELOPMENT.md	Updates module description to include timed field-index creation.

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