connectd: only charge gossip queries against the CPU budget

[nGoline]

This fixes CI after the gossip CPU throttle that shipped in v26.06.8. Since that change, valgrind runs fail on multi-peer offers tests (test_offer_with_private_channels_multyhop2, test_renepay.py::test_offers and test_offer_paths failed on #9582) with:

UNUSUAL connectd: That's weird: Throttling outgoing peer ...: too much CPU

The throttle is meant to bound the work of answering gossip queries, but it charged much more than that:

• on the way in, every message connectd handles itself (pings, pongs, onion messages, custom messages, gossip forwarded to gossipd), not only query_channel_range / query_short_channel_ids;
• on the way out, every check for pending query replies, which runs each time a peer's output queue drains, even with no query in flight;
• the budget is split evenly across all connected peers, so on a node with many peers each share is tiny and those charges use it up.

Under valgrind those charges add up quickly, and the same thing happens on busy mainnet nodes: connectd stops reading from a peer for a second or more, which also delays its channel messages.

Commits:

1. lightningd: add --dev-gossip-cpu-budget: sets only the CPU budget. --dev-throttle-gossip also shrinks the traffic limits, so a test using it can't tell which limit throttled a peer.
2. tests: ordinary messages must not count against the gossip CPU budget (xfail(strict=True)): 200 pings to a node with a 10 usec budget and the normal traffic limits must not get the peer throttled.
3. connectd: only charge gossip queries against the CPU budget: charge only reading the two query messages and answering them while one is pending (onion messages already have their own per-peer ratelimit), keep the even per-peer split with no minimum share (a minimum would let enough peers claim more than the whole budget), and log throttling once at debug. Removes the xfail.

Answering queries still counts, so test_gossip_query_channel_range_cpu_throttle still sees a flood of queries throttled.

Testing (docker):

• the new test fails before the fix with Throttling incoming/outgoing peer ...: too much CPU on pings alone, and passes after it;
• test_gossip.py (59 passed), test_askrene.py (37), test_xpay.py (35), all throttle tests, source checks;
• under VALGRIND=1: test_offer_with_private_channels_multyhop2, test_renepay.py::test_offers and test_offer_paths pass.

🤖 Generated with Claude Code

[jaonoctus]

I see you didn't sign the commits this time, not sure if that's intentional. Other than that, lgtm