turbocsv schema / infer: detect column types and export schema

[bytebrujo]

Proposal

Emit detected column types and an exportable schema.

turbocsv schema data.csv --format json-schema
turbocsv schema data.csv --format ts   # TypeScript interface

Notes

• The type-coercion engine in src/ts/row.ts already does the detection work.

Acceptance

• Infers string/number/boolean/date/currency/percent per column
• JSON Schema + TS interface output
• Tests