Lay groundwork for Phase 3 of the workspace split (improvise-8zh): a new
`crates/improvise-io/` sub-crate that will house the persistence and
import layers once the files move in the next commit.
Only scaffolding here:
- New `crates/improvise-io/Cargo.toml` declares deps on improvise-core,
improvise-formula, and the external crates persistence+import already
use: anyhow, chrono, csv, flate2, indexmap, pest, pest_derive, serde,
serde_json. Dev-deps: pest_meta, proptest, tempfile.
- New `crates/improvise-io/src/lib.rs` re-exports the core modules under
their conventional names (`format`, `model`, `view`, `workbook`,
`formula`) so in the next commit the moved code's `crate::model::*`,
`crate::view::*`, `crate::workbook::*`, `crate::format::*`, and
`crate::formula::*` paths resolve unchanged.
- Root `Cargo.toml` adds the new crate to workspace members and the main
crate's `[dependencies]`, ready to receive the move.
No source files change yet; cargo check --workspace still compiles as
before.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
