Corrections first, tuning second:

  - applies the core LimitRequestFields and LimitRequestFieldSize to
    HTTP/3 requests, which nothing did before, and advertises the bound
    as SETTINGS_MAX_FIELD_SECTION_SIZE instead of nghttp3's (1<<62)-1
  - bounds a response that makes no progress (H3StreamTimeout) so a
    client that stops reading cannot hold a worker thread, and closes a
    connection past H3MaxStreamErrors
  - advertises a QPACK dynamic table (H3QpackTableCapacity,
    H3QpackBlockedStreams); it was disabled, so HTTP/3 compressed
    request headers worse than HTTP/2 on the same server
  - exposes the request worker pool (H3MinWorkers, H3MaxWorkers,
    H3MaxWorkerIdleSeconds), previously hardcoded at 16/64
  - resolves mod_logio once instead of once per request