v0.1.373 — len(s.encode()) → UTF-8 byte length (PMAT-674)

Capability / correctness (PMAT-674): len(s.encode()) now transpiles to the UTF-8 byte length of a string (s.len()). s.encode() defaults to UTF-8, so len(s.encode()) equals Rust String::len() — distinct from len(s), which counts Unicode code points (.chars().count()). .encode() is otherwise an unsupported method call, so the whole idiom rejected; it's now detected in the len() intercept and routed to Expr::Len over the receiver. Accepts a bare .encode() or an explicit utf-8/utf8 literal arg. Found by the HUNT-V5 differential hunt; verified vs python3 (café → 5 bytes / 4 chars, € → 3 bytes). 431 e2e fixtures.