feat(client): add --timeouts option for session-opening retry schedule

docs/irtt-client.md

@@ -180,6 +180,12 @@ expansion: a hostname producing both families consumes two target slots.
 be greater than zero; a zero test duration, including `0s`, selects continuous
 mode.
 
+`--timeouts 1s,2s,4s,8s` sets the session-opening retry schedule. Each
+comma-separated duration is the receive timeout for one open attempt; attempts
+stop when a valid open reply arrives. The list must be nonempty, with each
+value at least `200ms`, and uses the same duration syntax as `--interval`.
+Omitting the option preserves the library default schedule.
+
 `--duration` controls the run length:
 
 - Any nonzero duration (default `10s`) is a **finite** run: probing stops

docs/irtt-tui.md

@@ -16,9 +16,9 @@ At least one target is required.
 
 Target syntax, multiple targets, and pacing are identical to
 `irtt-client(1)` — see that manual for `[LABEL=]TARGET` syntax and the
-`--pacing staggered|burst` option. The full set of negotiation flags
-(`--interval`, `--length`, `--hmac`, `--clock`, `--tstamp`, `--stats`,
-`--sfill`, `--dscp`, `--ttl`, `--loose`) is shared with `irtt-client` as
+`--pacing staggered|burst` option. The client configuration flags
+(`--interval`, `--timeouts`, `--length`, `--hmac`, `--clock`, `--tstamp`,
+`--stats`, `--sfill`, `--dscp`, `--ttl`, `--loose`) are shared with `irtt-client` as
 well; consult that manual for their meaning.
 
 Address-family controls are shared too: `-4` / `--ipv4` uses IPv4 only,