Move error classes from services/ and file-operations/ into a new errors/
directory (authentication-error, server-version-mismatch-error,
sync-reset-error, file-not-found-error), plus add file-already-exists-error
and http-client-error. Update consts.ts and utils/* (await-all,
create-client-id, hash, rate-limit, find-matching-file). Replace
data-structures (locks, min-covered, event-listeners, fix-sized-cache) and
add debugging utilities (in-memory-file-system, log-to-console,
slow-web-socket-factory). Removes utils/create-promise.ts.
