Add more TS/Rust snippets

[prrao87]

• TS/Rust snippets for data ingestion
• TS/Rust snippets for schema evolution. Fixes [typescript]: Missing typescript examples for schema evolution #178
  • Added full TypeScript schema evolution snippets (setup, add, alter, drop)
  • Added full Rust schema evolution snippets (same coverage)
  • Added expression-based type change examples (Python/TS/Rust): add derived column from SQL expression, drop old, rename new.
  • Added explicit vector dimension-change workaround examples for TS/Rust (FixedSizeList(384 -> 1024)): addColumns/add_columns + dropColumns/drop_columns + rename.
  • Added/updated warnings and prose to explain that alterColumns/alter_columns cannot directly cast across FixedSizeList dimension changes.