feat(wren-core-wasm): add registerCsv to load CSV data

[goldmedal]

Summary

Mirror registerJson / registerParquet for CSV. WASM SDK callers can now load CSV tables in-browser without pre-converting to JSON or Parquet.

// Inferred schema, defaults (header=true, comma, double-quote)
await engine.registerCsv('orders', 'id,amount\n1,100\n2,200');

// Or with full control
await engine.registerCsv('metrics', csvBytes, {
  header: false,
  delimiter: ';',
  quote: "'",
  schema: [
    { name: 'id', type: 'int64' },
    { name: 'amount', type: 'float64' },
  ],
});

Implementation

• Rust (core/wren-core-wasm/src/lib.rs): #[wasm_bindgen(js_name = registerCsv)] register_csv(&self, table_name, data: &[u8], options_json: &str). Options deserialize from JSON (deny_unknown_fields). Schema-from-columns mapper handles common Arrow types case-insensitively. Single-byte options reject non-ASCII to avoid slicing a UTF-8 codepoint.
• TypeScript (sdk/src/index.ts): async registerCsv(name, data: string | BufferSource, options?: CsvReadOptions). JS-side serializes options + encodes strings → UTF-8 bytes.
• Enabled csv feature on the arrow crate.

Options (camelCase)

Field	Type	Default
header	boolean	true
delimiter	string (1 ASCII char)	,
quote	string (1 ASCII char)	"
escape	string (1 ASCII char)	unset
terminator	string (1 ASCII char)	\n / \r\n
batchSize	number	8192
inferRows	number	1000
schema	[{name,type,nullable?}]	inferred

Type names mapped to Arrow (case-insensitive): int8/int16/int32/int64, uint*, float32/float64, boolean, string/utf8/varchar/text, date/date32/date64, timestamp/timestamp_{s,ms,us,ns}.

Test plan

• just build — wasm-pack + dist builds clean (72.3 MB)
• just test — all 27 SDK tests pass (6 new for registerCsv)
• just typecheck — TypeScript types compile clean
• cargo clippy --all-targets — no warnings
• cargo test --lib test_arrow_schema_from_columns_maps_aliases — passes
• wasm-pack test --node (CI; 6 new register_csv wasm-bindgen tests)

PR target

Targets feat/wasm-cube so it ships alongside the rest of the cube work.

---

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • CSV data support: Register and query CSV data with customizable options including delimiters, header configuration, and explicit schema definition
  • New CSV quickstart example and updated documentation guide users through CSV registration and data querying

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@core/wren-core-wasm/README.md`:
- Around line 195-198: The schema type list is missing the supported type
"date32"; update the documentation entry that enumerates Schema column types
(the line listing `date`/`date64`, `timestamp` etc.) to include `date32`
alongside the other date types so the README matches the SDK/Rust implementation
and avoids confusion for users defining CSV schemas.

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Configuration used: Repository UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 15a5950 and 56f725b.

📒 Files selected for processing (7)

• core/wren-core-wasm/AGENT_GUIDE.md
• core/wren-core-wasm/Cargo.toml
• core/wren-core-wasm/README.md
• core/wren-core-wasm/sdk/src/index.ts
• core/wren-core-wasm/sdk/src/wren_core_wasm.d.ts
• core/wren-core-wasm/sdk/tests/index.test.mjs
• core/wren-core-wasm/src/lib.rs