Upgrade and rate-limit compression failure message.

Without this message getting logged at 'WARN', it's hard to
contextualize the messages we get about compression bombs, so this
message should fix #40175.

I'm rate-limiting this, however, since it _could_ get spammy if
somebody on the network starts acting up.  (Right now it should be
very quiet; I've asked Sebastian to check it, and he says that he
doesn't hit this message in practice.)

Closes #40175.

src/feature/dirclient/dirclient.c

@@ -1944,7 +1944,9 @@ dir_client_decompress_response_body(char **bodyp, size_t *bodylenp,
   /* If we're pretty sure that we have a compressed directory, and
    * we didn't manage to uncompress it, then warn and bail. */
   if (!plausible && !new_body) {
-    log_fn(LOG_PROTOCOL_WARN, LD_HTTP,
+    const int LOG_INTERVAL = 3600;
+    static ratelim_t warning_limit = RATELIM_INIT(LOG_INTERVAL);
+    log_fn_ratelim(&warning_limit, LOG_WARN, LD_HTTP,
            "Unable to decompress HTTP body (tried %s%s%s, on %s).",
            description1,
            tried_both?" and ":"",