[Kinfe123]

Closes #102.

Problem

Cohere v2 streams tool calls as indexed start/delta/end events. Its TypeScript SDK also converts wire tool_calls fields to toolCalls, so a consumer that only understands the wire shape silently misses SDK arguments.

Change

Add streamfold/cohere, using the existing integration and parser pool. Accept both the SDK and decoded wire envelopes, correlate indexes with tool IDs, and finalize at tool-call end or EOF. Ignore text and tool-plan events; reject malformed input and generation error messages while releasing active parsers. Cohere remains a development-only dependency.

Verification

• Four focused tests cover the actual Cohere 8.3.0 SDK's SSE decoding and field conversion, interleaved calls, immutable partial values, duplicate ends, reused indexes, initial arguments, EOF, parser limits, malformed input, errors, and unmatched diagnostics.
• pnpm typecheck includes CohereClientV2.chatStream() passed directly to readStructured and manual consumption.
• pnpm release:check: 201 JavaScript tests and 11 Rust tests pass, plus type/syntax, WASM, formatting, Clippy, and package checks.
• The real SDK uses a deterministic fetch response in conformance tests. No live model request or speedup claim is involved.

Public surface

Adds streamfold/cohere, cohere, createStructuredStream, and CohereToolCallEvent. Updates README/API documentation and the unreleased changelog. No existing export or runtime dependency changes.

[Kinfe123]

lgtm, cohere sdk and wire events preserve streamed tool arguments.