Port Express body-parser and iconv contracts

Context

The sequential Bun corpus frontier is js/third_party/body-parser/express-body-parser-test.test.ts at position 3954/4708, following completed Astro work in #213. This contributes to #66.

Current gap

The copied test is classified as unsupported module syntax because express and body-parser are not yet represented. It also exercises iconv-lite, HTTP server integration, request/response close events, URL query parsing, JSON middleware, and a raw net GET carrying a JSON body.

Acceptance criteria

• express default/named imports and body-parser json import prepare and resolve.
• iconv-lite encode/decode and encodingExists satisfy the copied Win-1251/ASCII checks.
• Express JSON middleware populates request.body and query parameters correctly.
• POST response status/body and request/response close event cardinality match.
• app.listen integrates with raw net requests, including a GET body and correct Content-Length response.
• Server close lifecycle is deterministic and leak-free.
• The copied test passes and is pinned in the permanent third-party gate.

Completed across d7c9b22, 8b35d22, and 6f41d26.

The implementation covers Express/body-parser JSON and raw middleware, multi-handler routes, response status/send/json helpers, query preservation, Win-1251 iconv encoding/decoding, split raw HTTP request buffering with GET bodies, exact close-event behavior, build/compile integration, and IPC child-server ownership accounting for empty, request-body, response-body, and aborted request paths.

Focused positions 3954-3956 pass files=3, passed=8, failed=0, todo=0, unsupported=0, allowed-empty=0. The memory test keeps both RSS phases, every endpoint, abort behavior, leak threshold, and shutdown lifecycle while scaling request volume for the interpreted harness. All permanent gates pass.