[codex] Fix IMAP fetch when BODY precedes UID

[mpscholten]

Summary

Fix IMAP.fetch returning an empty ByteString when a UID FETCH response contains BODY[] before the server-supplied UID item.

The previous lookup' implementation assumed parsed fetch keys needed their first two words dropped, which only worked for the older parser artifact where keys looked like UID <n> BODY[]. When the response key is simply BODY[], the lookup misses and fetch falls back to BS.empty.

This change normalizes fetch keys before comparison, preserving compatibility with the UID <n> prefix form while also matching direct BODY[] keys, BODY.PEEK[], and origin suffixes such as BODY[]<0>.

Tests

• nix shell nixpkgs#haskell.compiler.ghc948 nixpkgs#cabal-install --command cabal test imap-parsers --test-show-details=direct