feat(quic): per-algorithm congestion-control tuning

[Itsusinn]

Summary

Today each backend only exposes a congestion-control algorithm name. This PR threads a backend-neutral CongestionTuning through TransportConfig so each backend can apply per-algorithm knobs, surfacing quiche's flow-control / CC tuning (including the full experimental BBR parameter set) and quinn's NewReno loss factor.

These types back the breeze tuic-server's new [backend.<backend>.cc] config sections (algo + per-algorithm sub-tables).

What's added

patches/tokio-quiche

• QuicSettings: new enable_cubic_idle_restart_fix: bool and custom_bbr_params: BbrParamsField, applied in make_quiche_config.
• BbrParamsField is a thin newtype over Option<quiche::BbrParams> — the #[settings] macro requires every field to impl Settings, which quiche::BbrParams doesn't (no serde), so the wrapper supplies trivial impls (the field is #[serde(skip)]).
• set_custom_bbr_params is gated behind quiche's internal feature; the call is guarded by #[cfg(feature = "quiche_internal")].

wind-quic

• Backend-neutral, serde-able Bbr2gcConfig (full ~26-field quiche BbrParams surface) + BbrBwLoReductionStrategy.
• CongestionTuning aggregate (initial cwnd packets, pacing, max pacing rate, HyStart++, CUBIC idle-restart-fix, BBR params) added to TransportConfig.
• quiche backend maps it onto QuicSettings (converting the neutral BBR config to quiche::BbrParams).
• Enables the tokio-quiche quiche_internal feature so set_custom_bbr_params is available.

wind-tuic

• quiche ConnectionOpts carries CongestionTuning (passed through to_transport).
• quinn inbound opts gain newreno_loss_reduction_factor.
• Re-exports the neutral config types for config front-ends.

Compatibility

No behavior change for existing callers: every new knob is Option-typed and defaults to leaving the backend default in place. The vendored crates/tuic-server adapter is updated for the new ConnectionOpts field (cc: Default::default()).

Test plan

• cargo check -p tuic-server --features quiche --all-targets (wind workspace) — green.
• cargo clippy -p wind-quic -p wind-tuic --features wind-tuic/quiche,wind-tuic/server — clean.
• cargo tree confirms quiche_internal is enabled on the resolved tokio-quiche, so set_custom_bbr_params is compiled in.

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will not alter performance

✅ 22 untouched benchmarks
⏩ 11 skipped benchmarks¹

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_{Comparing feat/cc-per-algorithm-tuning (7f57eb9) with main (b2ffb86)}

Footnotes

1. 11 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩