README and SPEC say a client too slow to send its request line and headers may get 400 (closes #138)

A client too slow to send its request line and headers within
SWWAF_CLIENT_REQUEST_TIMEOUT gets either no answer or, depending on how
much of them had arrived, 400 Bad Request from Go's server; either way
its connection is closed, nothing reaches the app, and no request log
line is written. The README's "Request log" and SPEC's size and time
limits said such a client always gets no answer. Both documents'
summaries of answers gave 408 for any slow client, when it is only for
a slow body.

Model: opus-5-5

SPEC.md

@@ -437,10 +437,10 @@ The settings, by group:
       the app sends it and the client receives it.
     - When a limit is passed before the response has started, `smallwebwaf`
       answers itself: `413` for a request body that is too large, `408` for a
-      client that is too slow, `502` for a response that is too large, `504` for
-      an app that is too slow. A request that announces a body larger than its
-      limit is refused before anything reaches the app. Once the response has
-      started it can only be cut off, and the connection is closed.
+      client too slow to send its body, `502` for a response that is too large,
+      `504` for an app that is too slow. A request that announces a body larger
+      than its limit is refused before anything reaches the app. Once the
+      response has started it can only be cut off, and the connection is closed.
     - Since a request body streams through, each side can hold up the other: a
       slow client slows the send to the app, and an app slow to take the body
       slows the client's send. So while a request body is still on its way, a
@@ -450,10 +450,12 @@ The settings, by group:
       waiting for the app to take what it had.
     - Go's HTTP server, on which `smallwebwaf` is built, reads a request's line
       and headers before `smallwebwaf` sees the request. A client that takes
-      longer than `SWWAF_CLIENT_REQUEST_TIMEOUT` to send them gets no answer:
-      the server closes its connection. Headers over
-      `SWWAF_CLIENT_REQUEST_HEADER_MAX_BYTES` are answered `431` by the server
-      itself. Neither request gets a line in the request log.
+      longer than `SWWAF_CLIENT_REQUEST_TIMEOUT` to send them gets either no
+      answer or, depending on how much of them had arrived, `400 Bad Request`
+      from the server; either way the server closes its connection and nothing
+      reaches the app. Headers over `SWWAF_CLIENT_REQUEST_HEADER_MAX_BYTES` are
+      answered `431` by the server itself. Neither request gets a line in the
+      request log.
     - A WebSocket connection leaves these limits behind once it is upgraded: it
       stays open until either side closes it.
 - Lookup of AS number and country (R7). On by default through GeoJS, which needs