chanbackup with many peers can do more than 128 concurrent rpc commands.
autoclean is the other plugin which can do many requests at once, so I
expect a similar issue there.
I tested this by rebuilding with `MAX_ACTIVE_SPANS` 1, which autoclean
tests triggered immediately.
The real fix is probably to use a hash table with a large initial size.
```
Mar 24 06:30:45 mlbb2 sh[28000]: chanbackup: common/trace.c:190: trace_span_slot: Assertion `s' failed.
Mar 24 06:30:45 mlbb2 sh[28000]: chanbackup: FATAL SIGNAL 6 (version v25.02)
Mar 24 06:30:45 mlbb2 sh[28000]: 0x5575232bac4f send_backtrace
Mar 24 06:30:45 mlbb2 sh[28000]: common/daemon.c:33
Mar 24 06:30:45 mlbb2 sh[28000]: 0x5575232baceb crashdump
Mar 24 06:30:45 mlbb2 sh[28000]: common/daemon.c:78
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958cd851f ???
Mar 24 06:30:45 mlbb2 sh[28000]: ./signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958d2c9fc __pthread_kill_implementation
Mar 24 06:30:45 mlbb2 sh[28000]: ./nptl/pthread_kill.c:44
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958d2c9fc __pthread_kill_internal
Mar 24 06:30:45 mlbb2 sh[28000]: ./nptl/pthread_kill.c:78
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958d2c9fc __GI___pthread_kill
Mar 24 06:30:45 mlbb2 sh[28000]: ./nptl/pthread_kill.c:89
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958cd8475 __GI_raise
Mar 24 06:30:45 mlbb2 sh[28000]: ../sysdeps/posix/raise.c:26
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958cbe7f2 __GI_abort
Mar 24 06:30:45 mlbb2 sh[28000]: ./stdlib/abort.c:79
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958cbe71a __assert_fail_base
Mar 24 06:30:45 mlbb2 sh[28000]: ./assert/assert.c:94
Mar 24 06:30:45 mlbb2 sh[28000]: 0x7f2958ccfe95 __GI___assert_fail
Mar 24 06:30:45 mlbb2 sh[28000]: ./assert/assert.c:103
Mar 24 06:30:45 mlbb2 sh[28000]: 0x5575232ab7fa trace_span_slot
Mar 24 06:30:45 mlbb2 sh[28000]: common/trace.c:190
Mar 24 06:30:45 mlbb2 sh[28000]: 0x5575232abc9f trace_span_start
Mar 24 06:30:45 mlbb2 sh[28000]: common/trace.c:267
Mar 24 06:30:45 mlbb2 sh[28000]: 0x5575232a7c34 send_outreq
Mar 24 06:30:45 mlbb2 sh[28000]: plugins/libplugin.c:1112
```
Changelog-Fixed: autoclean/chanbackup: fixed tracepoint crash on large number of requests.
Fixes: https://github.com/ElementsProject/lightning/issues/8177
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
ee2ec8befa